Many people derive peace of mind and purpose in life from their belief in God. For others, however, religion provides unsatisfying answers. Are there brain differences between believers and nonbelievers? Here we show that religious conviction is marked by reduced reactivity in the anterior cingulate cortex (ACC), a cortical system that is involved in the experience of anxiety and is important for self-regulation. In two studies, we recorded electroencephalographic neural reactivity in the ACC as participants completed a Stroop task. Results showed that stronger religious zeal and greater belief in God were associated with less firing of the ACC in response to error and with commission of fewer errors. These correlations remained strong even after we controlled for personality and cognitive ability. These results suggest that religious conviction provides a framework for understanding and acting within one's environment, thereby acting as a buffer against anxiety and minimizing the experience of error.