Objective: We examined differences in salient beliefs about physical activity (PA) and their influence on PA intention and behavior among South Korean university students before and during the COVID-19 pandemic. Methods: We used the Theory of Planned Behavior as a basis for the study. We used a repeated cross-sectional design. We conducted elicitation studies, and main and followup surveys with South Korean university students at two time points during September-October 2018 (n = 234) and September-December 2021 (n = 199). We used content analysis to identify salient beliefs about PA; we used structural equation modeling to analyze relationships among salient beliefs, PA intention, and behavior. Results: Prior to the pandemic, salient beliefs such as ‘builds social relationships,’ ‘takes too much time,’ and ‘friends’ significantly predicted PA intention and behavior. During the pandemic, ‘improves health status,’ ‘family members,’ and ‘laziness’ were significant predictors of PA intention and behavior although students’ average weekly PA time was decreased by half during the pandemic. Conclusions: The findings highlight how salient beliefs can shift substantially across contexts. Identifying such changes may improve predictions of PA engagement among university students, not only in the post-pandemic era but also in preparation for potential future public health crises.