Previous studies suggest beneficial effects of aerobic exercise on executive functions, which are a core deficit in ADHD. The aim of the present fMRI study was to investigate the neural mechanisms underlying these effects. We used functional magnetic resonance imaging (fMRI) to examine the brain activity of individuals with ADHD before and after engaging in acute aerobic exercise. The results showed that exercise improved cognitive control and reduced symptoms of ADHD. These findings suggest that aerobic exercise may be a useful adjunctive treatment for ADHD.