The association between physical activity (PA) and atrial fibrillation (AF) remains unclear. We thus investigated association of PA with the development of AF. Type and duration data for PA were acquired from 211,992 AF-free individuals using the validated Korean version of the International Physical Activity Questionnaire Short From between March 2002 and December 2014. Individuals were divided into four groups according to self-reported PA level and previous international PA guidelines: no PA with a sedentary lifestyle, insufficient PA, sufficient PA, and health-enhancing PA. AF was diagnosed by annual 12-lead electrocardiogram. During a median follow-up of 5.6 years, AF occurred in 304 participants (annual AF incidence rate 2.5/10,000 person-years). After adjusting for age and sex, PA level was not associated with AF incidence (P for trend = 0.26). The multivariable-adjusted hazard ratios (95% confidence interval) for incidental AF was 1.00 (0.74-1.37) for the insufficient PA group, 1.34 (0.91-1.97) for the sufficient PA group, and 1.27 (0.72-2.23) for the health-enhancing PA group compared with the no PA group (P for trend = 0.18). Thus, our study does not support an association between the risk of AF and PA level in a young Korean population.