Our study points out that there is a discrepancy between the self-perceived levels of own MVPA and VPA and the perceived descriptive norms of peers’ MVPA and VPA. Adolescents underestimate the prevalence of sufficient MVPA and VPA, and thus perceived descriptive norms in MVPA and VPA are worse than levels of own MVPA and VPA. These findings indicate room for targeted intervention based on the social norms based approaches to increase the physical activity of adolescents or at least strengthen their actual positive behaviour.