A method for analyzing the complexity time course of event-related EEG data is presented. The percentage of EEG complexity during imagination of hand movement relative to that during reference period is calculated for quantifying ERD (event-related desynchronization). The method is applied to two sets of event-related EEG recorded from two subjects. The preliminary results suggest that the relative increase and decrease of event-related EEG complexity could be an indicator of ERD/ERS (event-related synchronization). Dynamic complexity measure provides another idea for analyzing event-related EEG.