This paper introduces an electroencephalography (EEG)-based, real-time, cortical rhythmic activity monitoring system which can monitor spatiotemporal changes of cortical rhythmic activity on a subject's cortical surface, with a high temporal resolution. In the monitoring system, a frequency domain inverse operator is preliminarily constructed, based on the subject's anatomical information and sensor arrangement, and then spectral current power at each cortical vertex is calculated for the Fourier transforms of successive sections of continuous data, when a particular frequency band is given. The first pilot system was applied to two human experiments: (1) cortical alpha rhythm changes induced by opening and closing eyes and (2) cortical mu rhythm changes originated from arm movements, demonstrating the feasibility of the system.