The aim of this study was to examine modifiable biological, psychological, behavioral and social-environmental correlates of physical activity among 1129 Norwegian 11-year-old children within a cross-sectional sample from the HEalth In Adolescents study. Physical activity was assessed by accelerometer, and weight and height were measured objectively. Age- and gender-specific cut-off points proposed by the International Obesity Task Force were used to define body mass index. Social-environmental variables were self-reported by questionnaire. Hierarchical regression (linear mixed models) revealed that normal weight children scored higher on percentage daily moderate-to-vigorous physical activity [% daily moderate to vigorous physical activity (MVPA)] than overweight/obese children (P<0.001). Self-efficacy (P<0.01) and perceived social support from friends (P<0.01) were positively associated with children's % daily MVPA, and a negative association was found for computer/game-use on weekends (P<0.01). A moderator effect of weight category (normal vs overweight/obese) in the relationship between computer/game-use on weekends and % daily MVPA was detected (P<0.05), reflecting that higher computer/game-use on weekends was associated with lower % MVPA among the overweight/obese, but not among the normal weight. Modifiable correlates from multiple domains accounted for 14% of the variance in % daily MVPA. Prospective and intervention studies are needed to examine whether these factors act as mediators for physical activity change in pre-adolescent children.