Characteristics of the optical feedback noise in semiconductor lasers under superposition of the HF (High Frequency) current were experimentally examined and theoretically analyzed. The feedback noise was mostly suppressed by superposition of HF current, but still remained when frequency of the HF current coincided with a rational number of the round trip time period for the optical feedback in experimental measurement. Theoretical analysis was also given to explain these characteristic based on the mode competition theory of the semiconductor laser.