This paper presents a new adaptive active filter for compensating harmonic voltages in electric power systems. In order to improve the control speed, the compensator provides a high-precision and high-speed compensation signal for eliminating the harmonic components. A new design method is proposed and various experimental results are presented. This method is based on a new principle using a high-speed DSP for the detection and prediction of the harmonic voltages. The adaptive compensation and the FFT processing are done in real time. The compensation has very good characteristics to instantaneous variations of load in the electric power system. Thus, it is possible to compensate such harmonic power as generated by flicker load. The control circuit is completely digitized using a DSP, and the interferences are suppressed at a high degree of precision. Therefore, it becomes possible to implement an economical high-precision adaptive active filter for electric power systems.