A self-favoring bias for physical activity (PA) was examined in a community-based sample of middle-aged and older adults (N= 3,211). Participants' actual level of PA relative to peers was compared with their perceived PA relative to peers. It was estimated that 38% were realistic, 46% self-favoring, and 16% other-favoring in their perceptions. Among participants whose actual PA level was similar to peers, increasing age was associated with a self-favoring bias. Among less and more physically active participants, however, age was not associated with this bias. Better self-rated health and being male were also associated with a self-favoring bias. These results suggest that a self-favoring bias for PA exists in a significant proportion of middle-aged and older adults, and it is more pronounced with increasing age, among those with better self-rated health, and among men.