An active power filter is required to have a high current control capability of tracking a time-varying current reference template. However, a steady-state current error always exists because the reference current varies in time. This paper proposes the application of adaptive digital signal processing to the current control of an active filter. It does not require any additional hardware, but it can automatically minimize the steady-state current error. Experimental results demonstrate the usefulness of the adaptive digital signal processing algorithm for improving the filter performance.