We report the results of two experiments designed to clarify the spatial and temporal characteristics of the positive deflection that follows the error related negativity (ERN) elicited to incorrect responses in speeded reaction time tasks. Principal components analysis (PCA) indicates that the positive deflection reported to follow the ERN is composed of two different components: (a) a fronto-central positive deflection that follows the ERN and shares its spatial distribution and (b) a P300. When accuracy was required of the participants, the ERN and the P300 were larger in amplitude than when speed and accuracy were equally weighted. On the other hand, the amplitude of the fronto-central positive component was not affected by the degree to which accuracy was stressed.