Eighteen randomized controlled trials including 1122 patients with knee osteoarthritis were included in this systematic review and meta-analysis comparing mind–body exercise (tai chi, yoga, or baduanjin) versus various control interventions (e.g., health education, physical therapy, no treatment). Pooled outcomes of interest included pain, stiffness, physical function, mental health, depression, 6-minute walk test (6-MWT), and timed up and go (TUG) test. Mind–body exercise significantly improved pain, stiffness, and physical function, as well as mental health and depression. Motor ability was enhanced with increased 6-MWT distance and reduced TUG time. These findings suggest that mind–body exercise is a safe and effective non-pharmacologic option to improve both physical and mental outcomes in patients with KOA.