In this work, we propose a low-complexity variable forgetting factor (VFF) mechanism for recursive least square (RLS) algorithms in interference mitigation applications. The proposed VFF mechanism employs a time average of the error correlation to automatically adjust the forgetting factor in order to ensure fast convergence and good tracking of the interference and the channel variations. Simulation results for a direct-sequence code-division multiple access (DS-CDMA) system are presented for nonstationary environments and show that the proposed VFF mechanism achieves superior performance to previously reported methods at a reduced complexity.