Physical activity may decrease the risk of dementia; however, conflicting findings exist. The purpose of the current meta-analysis was to investigate the relationship between physical activity and dementia risk based on physical activity type, amount, and intensity, and to propose an effective minimal physical activity amount for older adults. Forty-four studies were selected for the meta-analysis. Participation in high (a total of >2 hours of activity over the course of three sessions per week) and moderate (a total of >1 hour of activity over the course of two sessions per week) amounts of physical activity showed decreased dementia risks compared to physical inactivity. Vigorous exercise, regular exercise, leisure time physical activities, and gardening showed a positive effect toward lowering dementia risk, but walking was not associated with dementia risk. Physically inactive individuals had a higher dementia risk than those who participated in physical activity. Participation in physical activities produces a favorable effect toward lowering dementia risk. Participating in regular physical activity of >1 hour over the course of two sessions per week and avoiding physical inactivity are recommended for lowering dementia risk.