We examined coherence of auditory steady state responses (ASSRs) in magnetoencephalogram to an ongoing sinusoidal amplitude modulated tone presented to the subject's left ear while bursts of white noise of various intensities were presented to the right ear. The results showed a significant enhancement in the real part of coherence of ASSRs obtained from the right and left temporal regions by the presence of white noise of appropriate intensity. The observed stochastic resonance (SR) most likely occurred within the central nervous system, which is from lateral superior olive to medial geniculate body. Our finding may be quite important as mechanisms of SR in biological systems are mostly unknown.