This paper presents a simple prediction based current reference generation method for a four-wire active power filter. In the steady state the current reference is generated according to data collected during the previous period. However, during the transient state of the load the prediction is no longer valid. Thus, in order to maintain the effective harmonic filtering performance a computational control delay compensation method is used instead. The proposed method is verified by experimental tests in a laboratory with a microcontroller controlled four-wire active power filter prototype