The present study investigates whether performance monitoring and its electrophysiological indices in a choice reaction time task are modulated by affective information presented briefly prior to the critical stimuli. A flanker task known to elicit a sufficient number of performance errors was used and prior to each flanker stimulus a neutral, pleasant or unpleasant picture from the International Affective Picture System (IAPS) was shown. While behavioral performance to the flanker stimuli was hardly affected by the preceding affective information, the error-related negativity (ERN) of the event-related potential was modulated by affective information: Unpleasant IAPS pictures preceding a performance error led to an increased ERN amplitude compared to trials with neutral and pleasant IAPS pictures. These trial-by-trial modulations of electrophysiological markers of performance monitoring are discussed in terms of the possible influence of affective stimuli on monaminergic neuromodulatory transmitter systems.