In this article, we review recent findings of the effects of physical activities on the aging brain and cognitive functions, focusing on functional magnetic resonance imaging (fMRI) results, including resting-state functional magnetic resonance imaging (RS-fMRI) and task-based functional magnetic resonance imaging (TB-fMRI). Moreover, the present articles explored both cross-sectional studies and longitudinal studies that examined the brain function alterations induced by physical activity training, which included cardiovascular fitness/aerobic exercise training, Tai Chi training, resistance exercise/weight training, and coordination exercise training, using measured amounts of physical activity as assessment criteria, and taking into account cognitive-related physical activity responses. Results of these RS-fMRI studies showed that older adults that engaged in cardiovascular fitness and aerobic training showed evidence of increasing brain functions. Furthermore, these positive effects also extended to older adults engaging in Tai Chi training. Also, a few studies focused on resistance exercise training; however, the results of these investigations remain inconsistence and thus will require further confirmation in the future. Results of the TB-fMRI studies indicated that older adults with higher levels of cardiovascular fitness or those engaged in cardiovascular fitness training combined with coordination training, have gained beneficial effects regarding brain functions. Specifically, the positive effects of cardiovascular fitness could be found in both normal and pathological aging populations, including older adults with mild cognitive impairment (MCI). Older adults with higher amounts of physical activity benefited in their brain functions more than older cognitively intact adults, or those with a high risk for dementia. Collectively, the results of previous studies established an experimental basis for assessing positive relationships between physical activities and brain functions, revealing that physical activity approaches might induce different improved brain functions. The consequence of these reviews provides physical activity prescriptions and exercise models relevant to improving brain functions for older populations in the society of Taiwan.