Cognitive dissonance is the uncomfortable psychological feeling that arises when something is perceived as contradictory. In 1957, Leon Festinger first developed the theory of cognitive dissonance, which has since continued to be of interest for, among other things, decision-making, moral reasoning, motivation, politics, and science. This systematic review summarises six peer-reviewed studies that use functional magnetic resonance imaging (fMRI) to measure if there is increased activity in the anterior cingulate cortex (ACC) and dorsal anterior cingulate cortex (dACC) during cognitive dissonance in adults. Four studies tested cognitive dissonance during forced choices and two during counter-attitudinal behaviours. The overall fMRI results indicate increased activity in ACC and dACC to dissonance versus control conditions, but with some inconsistency on the exact locations in the brain.