The study aimed to compare differences in physical activity, the relationship between physical activity and body composition, and seasonal variation in physical activity in outpatients with anorexia nervosa (AN) and healthy controls. Physical activity (CM-AMT) and time spent in different intensities of 10 female individuals with AN and 15 female controls was assessed across three seasons along with the percentage body fat. The two groups did not differ in their physical activity and both demonstrated seasonal variation. The percentage body fat of individuals with AN, but not that of the controls, was negatively related to CM-AMT and time spent in low-moderate intensity activity (LMI). Seasonal variation in physical activity emerged with increases in engagement in LMI during the summer period for both groups. Possible interpretations of the finding that decreased physical activity was related to a normalization of percentage body fat in the individuals with AN are discussed and implications for treatment are highlighted.