The purpose of this study was to explore the validity of evidence for self-efficacy to regulate physical activity scale (SERPA) measurement using an exploratory latent variable approach. The objectives were to explore the dimensionality, temporal invariance, and external validity of scores produced by the SERPA, a modified version of the barriers self-efficacy scale. Data (N[subscript baseline]= 461 and N[subscript 30 days post-baseline] = 427) from the Well-Being and Physical Activity Study (ClinicalTrials.gov, identifier: NCT03194854), which deployed the Fun For Wellness intervention, were analyzed. A two-dimensional factor structure explained responses to the SERPA at baseline. There was evidence for at least partial strict temporal measurement invariance for this two-dimensional structure. There was evidence for external validity of the SERPA measurement as evidenced by group assignment (i.e. the intervention) exerting a direct effect on the proposed two-dimensional structure of latent self-efficacy to regulate physical activity in adults with obesity at 30 days post-baseline.