This cross-sectional study contributes to the literature on whether body dissatisfaction is a barrier/facilitator to engaging in physical activity and to investigate the impact of mass-media messages via computer-time on body dissatisfaction. High-school students (N = 1501) reported their physical activity, computer-time (homework/leisure) and body dissatisfaction. Researchers measured students’ weight and height. Analyses revealed that body dissatisfaction was negatively associated with physical activity on both genders, whereas computer-time was associated only with girls’ body dissatisfaction. Specifically, as computer-homework increased, body dissatisfaction decreased; as computer-leisure increased, body dissatisfaction increased. Weight-related interventions should improve body image and physical activity simultaneously, while critical consumption of mass-media interventions should include a computer component.