<p>    The Coronavirus Disease 2019 (COVID-19) pandemic caused many changes in society. In Japan, most universities switched to online classes in order to prevent the spread of COVID-19. However, this switch might have led to decreased physical activity and prolonged sedentary time in university students. Therefore, the aim of this study was to ascertain the physical activity in students attending universities that switched to online classes during the COVID-19 pandemic. This study also examined the relationship between levels of physical activity and social support. Participants were 822 students enrolled in a university in Tokyo, Japan that switched to online classes. An online questionnaire survey was conducted during August 4-11, 2020 and contained items related to physical activity and sedentary time from the International Physical Activity Questionnaire-Short Form. After screening, a total of 662 valid responses were included in the analysis. The results showed a median total physical activity of 1228.50 METs・min/week and a median sedentary time of 480.00 min/day. Students who were categorized as having low levels of physical activity also had lower social support scores. These results suggest the need to take measures to maintain the physical activity levels of university students while preventing the spread of COVID-19. Sharing opportunities that students can perceive as social support might be one possible solution.</p>