Research has begun to examine the neurocognitive processes underlying voluntary moral decision making, which involves engaging in honest or dishonest behavior in a setting in which the individual is free to make his or her own moral decisions. Employing event-related potentials, we measured executive control-related and reward-related neural processes during an incentivized coin-guessing task in which participants had the opportunity to voluntarily engage in dishonest behavior, by overreporting their wins to maximize earnings. We report four primary findings: First, the opportunity to deceive recruited executive control processes involving conflict monitoring and conflict resolution, as evidenced by a higher N2 and a smaller P3. Second, processing the outcome of the coin flips engaged reward-related processes, as evidenced by a larger medial feedback negativity (MFN) for incorrect (loss) than for correct (win) guesses, reflecting a reward prediction error signal. Third, elevated executive control-related neural activity reflecting conflict resolution (i.e., an attenuated executive control P3) predicted a greater likelihood of engaging in overall deceptive behavior. Finally, whereas elevated reward-related neural activity (the reward P3) was associated with a greater likelihood of engaging in overall deceptive behavior, an elevated reward prediction error signal (MFN difference score) predicted increased trial-by-trial moral behavioral adjustment (i.e., a greater likelihood to overreport wins following a previous honest loss than following a previous honest win trial). Collectively, these findings suggest that both executive control- and reward-related neural processes are implicated in moral decision making.