Event-related brain potentials (ERPs) were used to examine the neural correlates of proactive and reactive cognitive control within the context of the Dual Mechanisms of Control theory. Individuals performed the counting Stroop task and the proportion of congruent and incongruent trials was varied across blocks. The Stroop effect was smaller in the mostly incongruent block than in the mostly congruent block. The ERP data revealed a double dissociation between the medial frontal negativity (MFN) and the medial posterior negativity (MPN), where the amplitude of the MFN was greater in the mostly incongruent block and the amplitude of the MPN was greater in the mostly congruent block. The ERP data also revealed slow wave activity that distinguished the mostly incongruent and mostly congruent blocks. These findings support the idea that different regions of the cingulate and anterior frontal cortex underpin proactive and reactive control.