Objective To compare objectively measured physical activity in older adults with symptomatic knee osteoarthritis (OA) with similarly aged adults without osteoarthritis (OA) or knee symptoms from the general population. Methods We included people ages 50–85 years with symptomatic knee OA from the Osteoarthritis Initiative (OAI, n = 491), and ages 50–85 years from the general population using National Health and Nutrition Examination Survey (NHANES, n = 449) data. A uniaxial accelerometer was worn for ≥10 hours/day for ≥4 days in the NHANES group in 2003–2004 and in the OAI group in 2008–2010. We calculated time spent in moderate‐to‐vigorous physical activity (MVPA in minutes/day) and described differences in MVPA and demographic variables between the samples. We conducted matched‐pairs sensitivity analyses to further evaluate the role of potential confounders. Results Both cohorts had similarly low levels of physical activity in age‐ and sex‐specific strata. Time in MVPA ranged from a median of 1–22 minutes/day in people with symptomatic knee OA, and from 1–24 minutes/day in the general population without OA or knee pain. These results were similar in sensitivity analyses. Conclusion Time spent in MVPA was similarly low in those with symptomatic knee OA as in older adults without knee pain or OA.