The health benefits of moderate-to-vigorous intensity physical activity (MVPA) are well established. MVPA also plays a role in reducing adults' risk of developing certain cancers. Yet, few adults are sufficiently active. Based on the Health Belief Model (HBM), people who perceive themselves as being susceptible to health risks form intentions to take preventive actions. Whereas there is evidence that adults tend to have higher health risk perceptions when a family member is diagnosed with cancer, it is not clear if this predicts greater MVPA. Drawing on the HBM, we investigated the associations between perceived cancer severity, perceived cancer susceptibility, perceived PA benefits to reduce cancer risk, perceived PA barriers, and PA barrier self-efficacy with MVPA among adults with and without a family history of cancer. Data collected online from 493 adults (Mage=36 years) were analyzed using linear regression analysis controlling for body mass index, sex, and education. Perceived PA barriers (β=-.16), PA barrier self-efficacy (β=.31), and having a family member diagnosed with cancer were associated with MVPA (p<.05). Our findings do not support the notion that cancer risk perceptions are associated with MVPA, but do show that adults with family history of cancer engaged in more MVPA. Further, they corroborate findings from other studies that showed that adults who report less perceived PA barriers and greater PA barrier self-efficacy are more active, which may be taken as an argument for the inclusion of strategies to help adults' overcome perceived PA barriers and build PA barrier self-efficacy in MVPA interventions.