The present study investigated the role of causal attribution for performance monitoring in the medial frontal cortex. To this end, we compared internally and externally-caused errors in a selective attention task with respect to error-related EEG activity and error-induced adjustments of speed and attentional selectivity. Both error types evoked early negativities and later positivities in the response-locked event-related potential. However, whereas internally-caused errors caused posterror slowing, externally-caused errors were followed by reduced attentional selectivity. Moreover, the amount of reduced attentional selectivity was related to the amplitude of the early negativity on externally-caused errors. This suggests that posterror adjustments are initiated on the basis of perceived causality and, thus, causal attribution of errors.