This study examined whether an alignment of physical activity (PA) between osteoarthritis patients and their spouses, which was previously proven by accelerometry, might also be revealed by self-report. The PA of 28 cohabitating couples (58–83 years) was assessed by means of synchronous accelerometry (ActiGraph wGTX3-BT) and compared to their according self-reports in the German Physical Activity, Exercise, and Sport Questionnaire (BSA-F). Both methods were used to quantify the average weekly light PA, moderate to vigorous PA (MVPA), and total PA. Accelerometry revealed no differences in weekly light PA and total PA (p ≥ 0.187) between patients and spouses, whereas the patients’ spouses accumulated significantly more MVPA (p = 0.015). In contrast, the self-report did not reveal any differences between the two groups in terms of PA (p ≥ 0.572). Subsequent correlation analyses indicated that accelerometry data for mild PA and total PA were significantly correlated in couples (r ≥ 0.385, p ≤ 0.024), but MVPA was not (r = 0.257, p = 0.097). The self-reported PA data, on the other hand, did not indicate any significant correlation (r ≤ 0.046, p ≥ 0.409). The presented results give a first indication that an alignment of PA between osteoarthritis patients and their spouses is most likely to be detected by accelerometry, but not by self-report.