The reemergence of primitive reflexes (PRs) in older adults is associated with dementia and cognitive impairment. Recent experimental work suggests gentle sensorimotor exercises may halt or reverse PR's inverse development. These findings question whether physical activity (PA) is negatively related to PRs. This study aimed to test this relationship in 52 older adults aged 66 and over who were volunteers from seven Hungarian nursing homes. They were tested individually using the Senior Test, hand-grip strength, 13 PRs, and PA levels using the Global Physical Activity Questionnaire. Apart from upper and lower body flexibility, all functional fitness indices and PA were negatively related to the number of PRs. A bootstrapped multiple hierarchical linear regression revealed that only PA was a statistically significant predictor (p < 0.001) of the PRs, accounting for 41% of the variance. This study is the first to demonstrate a robust negative relationship between PA and PRs and a weak negative association with hand-grip strength and four elements of functionality in older adults. The implications of the results could be significant for developing interventions to prevent or delay PRs' inverse development, which is associated with adverse mental health in older adults.