Background: Physical inactivity is a global problem and patients with knee osteoarthritis (OA) are predisposed to inactivity and its health-related consequences. Current guidelines recommend exercise as primary treatment but whether this affects time spent physically inactive is unknown. The objective was to investigate changes in physical inactivity among individuals with knee OA following an educational and exercise program. Methods: Pragmatic prospective cohort study performed in six physical therapy clinics in Denmark offering a nationwide education and exercise program for knee OA. The program consists of physiotherapy guided education and group-based or home exercise sessions, performed biweekly for approximately eight weeks. The exercises target knee and hip joint stability as well as focus on increasing muscle strength. Primary outcome was time spent physically inactive (min/day), measured with a tri-axial accelerometer mounted on the lateral side of the thigh during the entire exercise program duration. OA symptoms were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS). Results: Thirty-two individuals with knee OA were analyzed. From baseline to post-intervention, no changes occurred in average time spent physically inactive (mean change: + 16.2 min [95% CI − 15.7 to 48.1]; P = 0.31), but statistically significant improvements in KOOS pain (+ 6.7 points [95% CI 2.3 to 11.0]; P = 0.0032) and KOOS function (+ 5.8 points [95% CI 1.9 to 9.7]; P = 0.0046) were found. Conclusions: Participating and completing a widely adopted education and exercise program are not associated with spontaneous improvements in physical inactivity despite changes in self-reported pain and function. Interventions specifically targeting physical inactivity are needed. Registration number: www.clinicaltrials.gov: NCT03125954.