<Page>

                                                             Exhibit 99.906cert

                     N-CSR FORM OF SECTION 906 CERTIFICATION

     THE FOLLOWING CERTIFICATION IS PROVIDED BY THE UNDERSIGNED CHIEF EXECUTIVE
OFFICER AND CHIEF FINANCIAL OFFICER OF EQUITRUST VARIABLE INSURANCE SERIES FUND
ON THE BASIS OF SUCH OFFICERS' KNOWLEDGE AND BELIEF FOR THE SOLE PURPOSE OF
COMPLYING WITH 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE
SARBANES-OXLEY ACT OF 2002.

                                  CERTIFICATION

     In connection with the Annual Report of EquiTrust Variable Insurance Series
Fund (the "Company") on Form N-CSR for the period ended December 31, 2003 as
filed with the Securities and Exchange Commission on Form N-CSR (the "Report"),
we, Dennis M. Marker and James W. Noyce, Chief Executive Officer and Chief
Financial Officer, respectively, of the Company, hereby certify, pursuant to 18
U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley
Act of 2002, that:

     1.     The Report fully complies with the requirements of Section 13(a) or
15(d) of the Securities Exchange Act of 1934, as amended; and

     2.     The information contained in the Report fairly presents, in all
material respects, the financial condition and results of operations of the
Company.


                                                 /s/ Dennis M. Marker
                                             -----------------------------------
                                             Name: Dennis M. Marker
                                             Title: Chief Executive Officer
                                             Date: 2/19/04


                                                 /s/ James W. Noyce
                                             -----------------------------------
                                             Name: James W. Noyce
                                             Title: Chief Financial Officer
                                             Date: 2/19/04