Prevalence of psychological symptoms among Chinese university students is relatively high globally, and most students cannot receive timely treatment. Therefore, exploring protective factors for these symptoms is crucial. In this study, the aim was to examine the independent and joint associations of physical activity (PA) and mindfulness with symptoms of depression, anxiety, and internet addiction. Due to the simplicity of implementation in a university context, a cross-sectional survey was conducted in China in 2022. Participants were recruited through online advertisements, in which 710 Chinese university students met the eligibility criteria and were included in the analysis. Participants were then classified into four groups according to their PA and mindfulness levels. Adjusted nominal logistic regression models controlled for age and sex were fitted to examine the independent and joint associations of PA and mindfulness with symptoms of depression, anxiety, and internet addiction. When examined independently, high PA was associated with lower odds of depressive, anxiety, and internet addiction symptoms, while high mindfulness was associated with lower odds of depressive symptoms. When examining the joint effect, compared to students with low PA and low mindfulness, those with high PA and low mindfulness had a lower risk of depressive and internet addiction symptoms, while students with high PA and high mindfulness reported the lowest odds of depressive, anxiety, and internet addiction symptoms. The current study found that a combination of PA and mindfulness was associated with a lower risk of psychological symptoms. Future studies are suggested to confirm the joint effects of PA and mindfulness on mental health using experiment design.