The error-related negativity (ERN) is thought to index an anterior cingulate (ACC) behavioral monitoring system. The feedback ERN (FRN) is elicited to error feedback when the correct response is not known, but also when a choice outcome is suboptimal and to passive reward prediction violation, suggesting that the monitoring system may not be restricted to actions. This study used principal components analysis to show that the ERN consists of a single central component whereas the reward prediction violation FRN is comprised of central and prefrontal components. A prefrontal component is also present in action monitoring but occurs later, at the error positivity latency. This suggests that ACC monitors both actions and events for reward prediction error. Prefrontal cortex may update reward expectation based on the prediction violation with the latency difference due to differential processing time for motor and perceptual information.