It is a widely held view that students’ epistemic beliefs influence the way they learn and think in any given context. However, in the science learning context, the relation between the sophistication of epistemic beliefs and success in scientific practice is sometimes ambiguous. Taking this inconsistency as a point of departure, we examined the relationships between students’ scientific epistemic beliefs (SEB), their epistemic practices, and hence their epistemic cognition in a computer simulation in classical mechanics. The 19 tenth grade students’ manipulations of the simulation, spoken comments, behavior, and embodied communication were screen and video-recorded and subsequently described and coded by an inductive approach. The screen and video recordings were triangulated with a stimulated recall interview to access a broader understanding of the dynamic processes of epistemic cognition. Our findings focusing on three different students reveal a dynamic pattern of interactions between SEB and knowledge, i.e., epistemic cognition, showing how epistemic cognition can be understood in a specific problem solving context due to the actions the student express.