The prevalence of diabetes and obesity in Aboriginal populations across North America is a cause for concern. Regular physical activity has been shown to mitigate these risk factors. Despite this, there is a limited body of research that assesses the physical activity behaviors of Aboriginal people in Canada. Further. no studies have applied Ajzen's Theory of Planned Behavior (TPB) to determine the social and cognitive motivations of Aboriginal peoples to engage in physical activity. The purpose of this mixed method research was to determine the physical activity behaviors and motivations of a population of First Nation adults. Data collection consisted of the completion of the TPB questionnaire (N = 53) as well as focus group interviews (N=12) to determine the physical activity behaviors and belief-based perceptions, as per the TPB, of First Nation adults as they relate to engaging in physical activity. The research was conducted with participation of the Westbank First Nation, an Okanagan Nation band located near Kelowna. British Columbia. Quantitative analysis using hierarchical regression was used to determine the motivations of First Nation adults to engage in physical activity. Qualitative data analysis methods were used to construct themes representing motivations for physical activity common to the research participants. Results offer partial support for using the TPB to understand the motivations of Westbank First Nation adults. Further. Westbank First Nation adults have unique beliefs and meanings related to physical activity compared to the general population.