Contemporary theories of motor control assume that motor actions underlie a supervisory control system which utilizes reafferent sensory feedbacks of actions for comparison with the original motor programs. The functional network of visuomotor action monitoring is considered to include inferior parietal, lateral and medial prefrontal cortices. To study both sustained monitoring for visuomotor incongruence and the actual detection of incongruence, we used a hybrid fMRI epoch-/event-related design. The basic experimental task was a continuous motor task, comprising a simple racing game. Within certain blocks of this task, incongruence was artificially generated by intermittent takeover of control over the car by the computer. Fifteen male subjects were instructed to monitor for incongruence between their own and the observed actions in order to abstain from their own action whenever the computer took over control. As a result of both sustained monitoring and actual detection of visuomotor incongruence, the rostral inferior parietal lobule displayed a BOLD signal increase. In contrast, the prefrontal cortex (PFC) exhibited two different activation patterns. Dorsolateral (BA 9/46) and medial/cingulate (BA 8, BA 32) areas of the PFC displayed a greater increase of activation in sustained monitoring, while ventrolateral PFC showed greater event-related activation for the actual detection of visuomotor incongruence. Our results suggest that the rostral inferior parietal lobule is specifically involved in the reafferent comparison of the test subjects' own actions and visually perceived actions. Different activation patterns of the PFC may reflect different frontoparietal networks for sustained action monitoring and actual detection of reafferent incongruence.