Abstract Negative attitudes/beliefs surrounding osteoarthritis, pain, and activity contribute to reduced physical activity in people with knee osteoarthritis (KOA). These attitudes/beliefs are assessed using self-report questionnaires, relying on information one is consciously aware of and willing to disclose. Automatic (ie, implicit) assessment of attitudes does not rely on conscious reflection and may identify features unique from self-report. We developed an implicit association test that explored associations between images of a person moving/twisting their knee (activity) or sitting/standing (rest), and perceived threat (safe vs dangerous). We hypothesised that people with KOA would have greater implicit threat–activity associations (vs pain-free and non-knee pain controls), with implicit attitudes only weakly correlating with self-reported measures (pain knowledge, osteoarthritis/pain/activity beliefs, fear of movement). Participants (n = 558) completed an online survey: 223 had painful KOA (n = 157 female, 64.5 ± 8.9 years); 207 were pain free (n = 157 female, 49.3 ± 15.3 years); and 99 had non-KOA lower limb pain (n = 74 female, 47.5 ± 15.04 years). An implicit association between “danger” and “activity” was present in those with and without limb pain (KOA: 0.36, 95% CI 0.28-0.44; pain free: 0.13, 95% CI 0.04-0.22; non-KOA lower limb pain 0.11, 95% CI −0.03 to 0.24) but was significantly greater in the KOA group than in the pain free (P < 0.001) and non-KOA lower limb pain (P = 0.004) groups. Correlations between implicit and self-reported measures were nonsignificant or weak (rho = −0.29 to 0.19, P < 0.001 to P = 0.767). People with painful KOA hold heightened implicit threat–activity associations, capturing information unique to that from self-report questionnaires. Evaluating links between implicit threat–activity associations and real-world behaviour, including physical activity levels, is warranted.