We investigate the optical magnetometer for AC magnetic fields at several tens of kilohertz. The sensor requires a DC magnetic field to enhance its sensitivity. In this study, at first, we calibrated the signal response of the sensor using coils. The linear response for applied an AC field was obtained, and its sensitivity was 0.4 nT at 20 kHz. Subsequently, signal responses are investigated for comparison with using permanent magnets applying a DC field. The signal intensity was slightly decreased to about 81% by using magnets. These results suggest the possibility of miniaturization and metal-free configuration of the optical magnetometer.