For undergraduate students, excessive screen time is associated with poorer mental health and greater perceived stress. Objective: The purpose of the present investigation was to determine the potential moderating influence of physical activity and sleep on the relationship between screen time and stress. Participants & Methods: A cross-sectional sample of 513 undergraduate students between Fall 2017 & Spring 2020 were given a questionnaire to assess perceived stress level, physical activity engagement, screen time, and sleep. Results: Stepwise hierarchical regression analyses identified that screen time, sleep, and the three-way interaction between screen time, sleep, and physical activity were associated with stress. Post-hoc decomposition revealed that higher levels of physical activity and sleep both mitigated the relationship between screen time and stress. Conclusions: Findings suggest that modifiable health behaviors such as physical activity and sleep may be important factors for managing the negative effects of screen time on stress in college-aged adults.