Few studies have explored the moderating effects of race on children's physical activity (PA) and psychosocial beliefs, particularly in physical education (PE) setting. The purpose of this study was to investigate whether children's PA behaviors and PA-related psychosocial beliefs differed as a function of race, as well as to explore any racial differences in the relationships between PA and PA-related beliefs. A total of 174 fourth and fifth grade children from two elementary schools in Minnesota participated in this cross-sectional study. During three PE sessions, children's percentages of time spent in sedentary behavior, light PA, and moderate-to-vigorous PA (MVPA) were measured via ActiGraph GT3X+ accelerometers. A number of validated questionnaires were used to assess the children's PA-related psychosocial beliefs (i.e., self-efficacy, outcome expectancy, social support, and enjoyment) at the end of the last (third) session. Our data suggested that African American children spent significantly less percentage of time in sedentary behavior than their white counterparts, F (2, 171) = 3.33, p = 0.04. African American children's light PA, F (2, 171) = 1.99, p = 0.14, and MVPA percentage, F (2, 171) = 2.76, p = 0.06, were slightly higher than those of the other two groups; however, the differences did not reach the significance level. This study suggests that African American children are less sedentary and hold higher PA-related outcome expectancy and social support beliefs than white children.