In recent decades, the number of adolescents and young adults with poor mental health has been increasing, particularly among students in tertiary institutions. This study investigates the physical activities, resilience, and mental health status of junior college students in Hong Kong. The questionnaire consisted of demographic characteristics, the Positive Mental Health Scale, the Brief Resilience Scale, and the Godin-Shephard Leisure-Time Physical Activity Questionnaire. Four hundred and sixteen students participated in the study. The results showed a moderate positive correlation (r = 0.485) between resilience and mental health, and a low positive correlation (r = 0.258) between resilience and physical activity. The one-way analysis of variance (ANOVA) with a post hoc test showed that arts students engaged in more physical activity than students from other disciplines. A multiple regression analysis was used to examine the predictors of a positive mental health status. The significant predictors are: resilience (β = 0.704; 95% CI = 0.575–0.833; P < 0.001), physical activity score (β = 0.032; 95% CI = 0.016–0.048; P < 0.001), the male gender (β = 1.035, 95% CI = 0.171–1.900; P < 0.05), and students’ enrollment in a health science discipline (β = 1.052, 95% CI = 0.175–1.930; P < 0.05). Preventive measures, such as strengthening resilience, a broad curriculum and taking note of the demographic and cognitive characteristics of students are essential for improving the mental health of freshmen in colleges.