The error-related negativity (ERN) is an event-related brain potential observed when subjects receive feedback indicating errors or monetary losses. Evidence suggests that the ERN is larger for unexpected negative feedback. The P300 has also been shown to be enhanced for unexpected feedback, but does not appear to be sensitive to feedback valence. The present study evaluated the role of expectations on the ERN and P300 in two experiments that manipulated the probability of negative feedback (25%, 50%, or 75%) on a trial-by-trial basis in experiment 1, and by varying the frequency of positive and negative feedback across blocks of trials in experiment 2. In both experiments, P300 amplitude was larger for unexpected feedback; however, the ERN was equally large for expected and unexpected negative feedback. These results are discussed in terms of the potential role of expectations in processing errors and negative feedback.