Physical activity is essential for a healthy development and for the well-being of young people. The present study is based upon the assumption that physical activity is influenced by psychological factors like the attribution of physical activity effects and self-efficacy, as well as by chronotype. Seven hundred and twenty-six adolescents participated in this study, and we applied the following scales: physical activity self-efficacy beliefs (PASE), positive attribution of physical activity (PAPA), and negative attribution of physical activity (NAPA), self-report physical activity level, and the Composite Scale of Morningness (CSM). PASE scores correlated with the positive attribution of physical activity effects but not with the negative attribution. Morning-oriented pupils were more physically active. Furthermore, there was a positive correlation between CSM and PASE. Also, morning-oriented pupils gave more positive attributes to the effects of physical activity. The results have an impact on programs devoted to increasing physical activity in adolescents.