Anxiety disorders are highly debilitating mental illnesses. They are characterized by heightened worry and physiological arousal that manifest as psychological, physiological, and behavioral disturbances. Critically, a large proportion of the population suffers from elevated anxiety. Although physical exercise has been proposed as a potential treatment for managing anxiety symptoms, the strength of this effect may vary depending on the anxiety severity of the sample at intervention onset. The present study examined the effect of moderate intensity aerobic exercise training on anxiety in young adults. We hypothesized that anxiety would be significantly lower after nine weeks of exercise training compared to no exercise training, and that this effect would be moderated by anxiety severity. Fifty-five inactive participants (47 females) were randomized into either an exercise group or a non-exercise control group. The exercise group completed three moderate intensity continuous aerobic exercise sessions per week for nine weeks, whereas the control group remained inactive. Anxiety was measured before and after the intervention using the Beck Anxiety Inventory. At the end of the intervention, the exercise group had significantly lower anxiety than the control group (p = .016). This effect was moderated by anxiety severity, such that the effect of exercise on post-intervention anxiety was only observed in individuals with high levels of anxiety at baseline [B = -10.60, SE = 3.48, p = .0037, CI = -17.59 to -3.60]. These findings point to regular aerobic exercise as an effective tool for young adults experiencing elevated anxiety to manage their symptoms.