The primary purpose of this study was to determine if the theory of planned behavior (TPB) mediated the relationship between selected personality traits (i.e., extroversion, neuroticism, and conscientiousness) and exercise behavior using structural equation modeling. Based on previous research, it was hypothesized that extroversion (E) would have a significant direct effect on exercise behavior while controlling for the TPB. A secondary purpose was to explore whether the facets of these personality domains had significant effects on TPB constructs or exercise behavior while controlling for the general personality domains. Female undergraduate students (N= 301) completed measures of the TPB, the Five-Factor model of personality, and a 1-month exercise behavior follow-up. Model 1 resulted in a direct effect of E on exercise behavior. Model 2 suggested a significantly better fit when direct effects of E's activity facet were freed for estimation. Moreover, freeing these effects rendered the effects of general E nonsignificant. It was concluded that the direct effect of E on exercise behavior found in previous research might be explained entirely by the activity facet of E.