Preparing to stop may “prime” the neural mechanism for stopping and alter brain activity at the time of stopping. Much electroencephalography (EEG) research has studied the N2/P3 complex over frontocentral electrodes during outright stopping. Here, we used differential reward of the stop and go processes in a stop signal task to study the sensitivity of these EEG components to preparation. We found that (a) stopping was faster when it was rewarded; (b) the P3 amplitude was larger for successful versus failed stopping, and this difference was greater when stopping was rewarded over going; (c) the N2 component was observed only on failed stop trials; and (d) there was greater EEG coherence between frontocentral and occipitoparietal electrodes at 12 Hz during the initiation of a go response when stopping was rewarded over going. We propose that frontocentral cortical mechanisms active before and at the time of stopping are sensitive to preparation.