
<PAGE>   1
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JANUARY 12, 1998
                                                           REGISTRATION NO. 333-

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      Under
                           The Securities Act of 1933

                         ------------------------------

                               ACT NETWORKS, INC.
             (Exact name of Registrant as specified in its charter)

                         ------------------------------

           DELAWARE                                       77-0396887
 (State or other jurisdiction                  (IRS Employer Identification No.)
of incorporation or organization)

                                 188 CAMINO RUIZ
                           CAMARILLO, CALIFORNIA 93012
               (Address of principal executive offices) (Zip code)
                         ------------------------------
                            1997 STOCK INCENTIVE PLAN

                            (Full title of the Plan)

                         ------------------------------
                                   MARTIN SHUM
                             CHIEF EXECUTIVE OFFICER
                               ACT NETWORKS, INC.
                  188 CAMINO RUIZ, CAMARILLO, CALIFORNIA 93012
                                 (805) 388-2474
          (Telephone number, including area code, of agent for service)


                         CALCULATION OF REGISTRATION FEE
================================================================================
<TABLE>
<CAPTION>

                                                    Proposed            Proposed
      Title of                                       Maximum             Maximum
     Securities                 Amount              Offering            Aggregate          Amount of
        to be                   to be                Price               Offering         Registration
     Registered              Registered(1)          per Share             Price                Fee
     ----------              -------------          ---------             -----                ---
<S>                        <C>                      <C>                <C>                   <C> 
Common Stock, 
$0.001 par value            460,000 shares          $9.00(2)           $4,140,000(2)         $1,221
</TABLE>

================================================================================
(1) This Registration Statement shall also cover any additional shares of Common
    Stock which become issuable under the 1997 Stock Incentive Plan or by reason
    of any stock dividend, stock split, recapitalization or any other similar
    transaction without receipt of consideration which results in an increase in
    the number of outstanding shares of Registrant's Common Stock.

(2) Calculated solely for purposes of this offering under Rule 457(h) of the
    Securities Act of 1933, as amended, on the basis of the average of the high
    and low selling prices per share of Common Stock of ACT Networks, Inc. on
    January 7, 1998, as reported on the Nasdaq National Market.


<PAGE>   2



                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE

    ACT Networks, Inc. (the "Registrant") hereby incorporates by reference into
this Registration Statement the following documents previously filed with the
Securities and Exchange Commission (the "SEC"):

    (a)    The Registrant's Annual Report on Form 10-K for the fiscal year ended
           June 30, 1997, filed with the SEC on September 30, 1997;

    (b)    The Registrant's Quarterly Report on Form 10-Q for the fiscal quarter
           ended September 30, 1997, filed with the SEC on November 14, 1997;

    (c)    The Registrant's Current Report on Form 8-K, as amended, filed with 
           the SEC on August 11, 1997; and

    (d)    The Registrant's Registration Statement No. 000-25740 on Form 8-A, as
           amended, filed with the SEC on March 23, 1995 in which the terms,
           rights and provisions applicable to the Registrant's Common Stock are
           described.

    All reports and definitive proxy or information statements filed pursuant to
Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 (the
"1934 Act") after the date of this Registration Statement and prior to the
filing of a post-effective amendment which indicates that all securities offered
hereby have been sold or which deregisters all securities then remaining unsold
shall be deemed to be incorporated by reference into this Registration Statement
and to be a part hereof from the date of filing of such documents. Any statement
contained in a document incorporated or deemed to be incorporated by reference
herein shall be deemed to be modified or superseded for purposes of this
Registration Statement to the extent that a statement contained herein or in any
subsequently filed document which also is deemed to be incorporated by reference
herein modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this Registration Statement.


ITEM 4.  DESCRIPTION OF SECURITIES

    Not applicable.


ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL

    Not applicable.


ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS

    Under Section 145 of the Delaware General Corporation Law, the Registrant
has broad powers to indemnify its directors and officers against liabilities
they may incur in such capacities, including liabilities under the Securities
Act of 1933, as amended (the "1933 Act"). The Registrant's Bylaws (the "Bylaws")
provide that the Registrant shall indemnify its directors and officers if such
officer or director acted (i) in good faith, (ii) in a manner reasonably
believed to be in or not opposed to the best interests of the Registrant, and
(iii) with respect to any criminal action or proceeding, had no reasonable cause
to believe such conduct was unlawful. The Registrant believes that
indemnification under its Bylaws covers at least negligence and gross
negligence, and requires the Registrant to advance litigation expenses in the
case of stockholder derivative actions

                                      II-2

<PAGE>   3



or other actions, against an undertaking by the directors and officers to repay
such advances if it is ultimately determined that the director is not entitled
to indemnification. The Bylaws further provide that rights conferred under such
Bylaws shall not be deemed to be exclusive of any other right such persons may
have or acquire under any agreement, vote of stockholders or disinterested
directors, or otherwise.

    In addition, the Registrant's Certificate of Incorporation (the "Certificate
of Incorporation") provides that, pursuant to Delaware law, none of its
directors shall be liable for monetary damages for breach of his or her
fiduciary duty of care to the Registrant and its stockholders. This provision in
the Certificate of Incorporation does not eliminate the duty of care, and in
appropriate circumstances equitable remedies such as injunctive or other forms
of non-monetary relief will remain available under Delaware law. In addition,
each director will continue to be subject to liability for breach of the
director's duty of loyalty to the Registrant for acts or omissions not in good
faith or involving intentional misconduct, for knowing violations of law, for
actions leading to improper personal benefit to the director, and for payment of
dividends or approval of stock repurchases or redemptions that are unlawful
under Delaware law. The provision also does not affect a director's
responsibilities under any other law, such as the federal securities laws or
state or federal environmental laws. The Certificate of Incorporation further
provides that the Registrant shall indemnify its directors and officers to the
fullest extent permitted by law and requires the Registrant to advance
litigation expenses in the case of stockholder derivative actions or other
actions, against an undertaking by the director to repay such advances if it is
ultimately determined that the director is not entitled to indemnification. The
Certificate of Incorporation also provides that rights conferred under such
Certificate of Incorporation shall not be deemed to be exclusive of any other
right such persons may have or acquire under any statute, the Certificate of
Incorporation, the Bylaws, agreement, vote of stockholders or disinterested
directors, or otherwise.

    The Registrant has obtained a liability insurance policy for the officers
and directors that, subject to certain limitations, terms and conditions, will
insure them against losses arising from wrongful acts (as defined by the policy)
in their capacity as directors or officers.

    In addition, the Registrant has entered into agreements to indemnify its
directors and certain of its officers in addition to the indemnification
provided for in the Certificate of Incorporation and Bylaws. These agreements,
among other things, indemnify the Registrant's directors and certain of its
officers for certain expenses (including attorneys fees), judgments, fines and
settlement amounts incurred by such person in any action or proceeding,
including any action by or in the right of the Registrant, on account of
services as a director or officer of the Registrant or as a director or officer
of any subsidiary of the Registrant, or as a director or officer of any other
company or enterprise that the person provides services to at the request of the
Registrant.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED

    Not applicable.


ITEM 8.    EXHIBITS

Exhibit No.       Exhibit
-----------       -------

    4      Instruments Defining Rights of Stockholders. Reference is made to
           Registrant's Registration Statement No. 000-25740 on Form 8-A, as
           amended, which is incorporated herein by reference pursuant to Item
           3(d) of this Registration Statement.

    5      Opinion and Consent of Brobeck, Phleger & Harrison LLP.

    23.1   Consent of Ernst & Young LLP, Independent Public Accountants.

    23.2   Consent of Brobeck, Phleger & Harrison LLP is contained in Exhibit 5.

    24     Power of Attorney. Reference is made to page II-5 of this
           Registration Statement.

    99.1   1997 Stock Incentive Plan.

    99.2   Form of Notice of Grant of Stock Option - Installment Option.

                                      II-3

<PAGE>   4



    99.3   Form of Stock Option Agreement - Installment Option.

    99.4   Notice of Grant of Stock Option - Immediately Exercisable Option

    99.5   Stock Option Agreement - Immediately Exercisable Option

    99.6   Form of Addendum to Stock Option Agreement (Limited Stock
           Appreciation Rights).

    99.7   Form of Addendum to Stock Option Agreement (Involuntary Termination
           following Change in Control).

    99.8   Stock Purchase Agreement

    99.9   Addendum to Stock Purchase Agreement (Involuntary Termination
           Following Change in Control)

    99.10  Automatic Notice of Initial Grant

    99.11  Automatic Notice of Annual Grant

    99.12  Automatic Stock Option Agreement

ITEM 9.  UNDERTAKINGS

    A. Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the indemnification provisions summarized in Item 6, or
otherwise, the Registrant has been advised that in the opinion of the Securities
and Exchange Commission such indemnification is against public policy as
expressed in the Securities Act, and is, therefore, unenforceable. In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a director, officer,
or controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling person
in connection with the securities being registered hereunder, the Registrant
will, unless in the opinion of its counsel the matter has been settled by
controlling precedent, submit to a court of appropriate jurisdiction the
question of whether such indemnification by it is against public policy as
expressed in the Securities Act and will be governed by the final adjudication
of such issue.

    B. The undersigned Registrant hereby undertakes: (1) to file, during any
period in which offers or sales are being made, a post-effective amendment to
this Registration Statement (i) to include any prospectus required by Section
10(a)(3) of the 1933 Act, (ii) to reflect in the prospectus any facts or events
arising after the effective date of this Registration Statement (or the most
recent post-effective amendment thereof) which, individually or in the
aggregate, represent a fundamental change in the information set forth in this
Registration Statement and (iii) to include any material information with
respect to the plan of distribution not previously disclosed in this
Registration Statement or any material change to such information in this
Registration Statement; provided, however, that clauses (1)(i) and (1)(ii) shall
not apply if the information required to be included in a post-effective
amendment by those paragraphs is contained in periodic reports filed by the
Registrant pursuant to Section 13 or Section 15(d) of the 1934 Act that are
incorporated by reference into this Registration Statement; (2) that for the
purpose of determining any liability under the 1933 Act each such post-effective
amendment shall be deemed to be a new registration statement relating to the
securities offered therein and the offering of such securities at that time
shall be deemed to be the initial bona fide offering thereof; and (3) to remove
from registration by means of a post-effective amendment any of the securities
being registered which remain unsold at the termination of the Registrant's 1997
Stock Incentive Plan.

    C. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the 1933 Act, each filing of the Registrant's
annual report pursuant to Section 13(a) or Section 15(d) of the 1934 Act that is
incorporated by reference into this Registration Statement shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.


                                               II-4

<PAGE>   5



                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, as amended, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Camarillo, State of California on January 12, 1998.


                                                ACT NETWORKS, INC.


                                                By: /s/ Martin Shum
                                                   -----------------------------
                                                    Martin Shum
                                                    Chief Executive Officer
                                                    and Chairman of the Board



                                POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS:

         That the undersigned officers and directors of ACT Networks, Inc., a
Delaware corporation, do hereby constitute and appoint Martin Shum and Melvin L.
Flowers and each of them, the lawful attorneys-in-fact and agents, with full
power and authority to do any and all acts and things and to execute any and all
instruments which said attorneys and agents, or either one of them, determine
may be necessary or advisable or required to enable said corporation to comply
with the Securities Act of 1933, as amended, and any rules or regulation or
requirements of the Securities and Exchange Commission in connection with this
Registration Statement. Without limiting the generality of the foregoing power
and authority, the powers granted include the power and authority to sign the
names of the undersigned officers and directors in the capacities indicated
below to this Registration Statement, to any and all amendments, both
pre-effective and post-effective, and supplements to this Registration Statement
and to any and all instruments or documents filed as part of or in conjunction
with this Registration Statement or amendments or supplements thereto, and each
of the undersigned hereby ratifies and confirms all that said attorneys and
agents, or either one of them, shall do or cause to be done by virtue hereof.
This Power of Attorney may be signed in several counterparts.

         IN WITNESS WHEREOF, each of the undersigned has executed this Power of
Attorney as of the date indicated.

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed below by the following persons in
the capacities and on the dates indicated.

<TABLE>
<CAPTION>

Signatures                   Title                             Date
----------                   -----                             ----
<S>                  <C>                                  <C>

/s/ Martin Shum      Chief Executive Officer              January 12, 1998
-------------------  and Chairman of the Board
Martin Shum          (Principal Executive Officer)
</TABLE>


                                      II-5

<PAGE>   6

<TABLE>
<CAPTION>

Signatures                                 Title                        Date
----------                                 -----                        ----
<S>                                 <C>                            <C>  


/s/ Melvin L. Flowers               Vice President Finance &       January 12, 1998
--------------------------------    Administration and Chief 
Melvin L. Flowers                   Financial Officer (Principal 
                                    Financial and Accounting 
                                    Officer)

/s/ Brig. Gen. Harold R. Johnson    Director                       January 12, 1998
--------------------------------
Brig. Gen. Harold R. Johnson



/s/ William Ambrose                 Director                       January 12, 1998
--------------------------------
William Ambrose



/s/ Archie J. McGill                Director                       January 12, 1998
--------------------------------
Archie J. McGill



/s/ Frederick Gluck                 Director                       January 12, 1998
--------------------------------
Frederick Gluck

</TABLE>





                                      II-6


<PAGE>   7



                                  EXHIBIT INDEX
<TABLE>
<CAPTION>

Exhibit
   No.       Exhibit
   ---       -------
<S>          <C> 
    4        Instruments Defining Rights of Stockholders. Reference is made to
             Registrant's Registration Statement No. 000-25740 on Form 8-A, as
             amended, which is incorporated herein by reference pursuant to Item
             3(d) of this Registration Statement.

    5        Opinion and Consent of Brobeck, Phleger & Harrison LLP.

    23.1     Consent of Ernst & Young LLP, Independent Public Accountants.

    23.2     Consent of Brobeck, Phleger & Harrison LLP is contained in Exhibit
             5.

    24       Power of Attorney. Reference is made to page II-5 of this
             Registration Statement.
  
    99.1     1997 Stock Incentive Plan.

    99.2     Form of Notice of Grant of Stock Option - Installment Option.

    99.3     Form of Stock Option Agreement - Installment Option.

    99.4     Notice of Grant of Stock Option - Immediately Exercisable Option

    99.5     Stock Option Agreement - Immediately Exercisable Option

    99.6     Form of Addendum to Stock Option Agreement (Limited Stock
             Appreciation Rights).
  

    99.7     Form of Addendum to Stock Option Agreement (Involuntary Termination
             following Change in Control).

    99.8     Stock Purchase Agreement 99.9 Addendum to Stock Purchase Agreement
             (Involuntary Termination Following Change in Control)
  
    99.10    Automatic Notice of Initial Grant

    99.11    Automatic Notice of Annual Grant

    99.12    Automatic Stock Option Agreement
</TABLE>


