Research is emerging illustrating the predictive effects of psychological mindsets on physical activity. The results of one study revealed that those who held a mindset that their physical activity was adequate for health, while controlling for current activity, reported more activity (Zahrt & Crum, 2020). Given mindset’s potential future importance, the first purpose was to replicate the positive relationship between perceived activity adequacy mindset and activity (Zahrt & Crum, 2020). The second purpose was to examine three factors that might inform individuals’ perceptions of whether their activity was adequate for health benefits – activity history, activity guideline knowledge, and activity social comparison. Participants completed two online surveys seven days apart. The first assessed demographic information, physical activity history, physical activity guideline knowledge, perceived activity adequacy mindset, and physical activity social comparison (n = 187). The second assessed current physical activity over the previous week (n = 135). Path analysis revealed that perceived activity adequacy mindset was positively associated with current physical activity. In terms of factors that might inform mindset, physical activity social comparison was directly, and physical activity history and physical activity guideline knowledge were indirectly associated with perceived activity adequacy mindset. The results provide additional evidence for a relationship between perceived activity adequacy mindset perceptions and physical activity as well as reveal some potential direct and indirect antecedents of perceived activity adequacy mindset. If replicated using an experimental design, recognition that mindset may influence physical activity engagement may be instructive in the formulation of future physical activity promotion materials.