We report an MEG (magnetoencephalography) study to investigate the neural correlates of a short-term memory for event duration. Participants were asked to mentally retain the event duration of an auditory stimulus. We examined the frequency characteristics of the neuromagnetic signals of the right IPL (intraparietal lobule) region during the retention of event duration. The results showed that the FFT power of 5, 15, and 20 Hz were associated with the length of an event only when the participants retained the duration information. These results suggest that the right IPL region may contribute to temporal memory processing, and that the frequency characteristics of neural signals play an important role in retaining event duration information.