Obese older people are more likely to be frail than those with a normal body mass index (BMI), but the results of individual studies have been inconsistent. We conducted a systematic review and meta-analysis to clarify the association between obesity and the risk of frailty, and whether there was a relationship between BMI and frailty, in community-dwelling older adults aged ≥60 years. Eight databases (PubMed/MEDLINE, EMBASE, EBSCO, CINAHL, Scopus, Cochrane Library and Web of Science) were systematically searched from inception to August 2020. Relative risks for incident frailty were pooled using a random-effects model. We found a positive association between abdominal obesity and frailty [relative risk (RR) = 1.57, 95% confidence interval (CI) 1.29–1.91, I2 = 48.1%, P = 0.086, six observational studies, 18,764 subjects]. People in the higher category of waist circumference had a pooled 57% higher risk of frailty than those with a normal waist circumference. In addition, a total of 12 observational studies comprising 37,985 older people were included in the meta-analysis on the relationship between BMI and the risk for frailty. Taking the normal BMI as the reference group, the pooled RR of frailty risk ranged from 1.45 (95% CI 1.10–1.90, I2 = 83.3%; P < 0.01) for the underweight group, to 0.93 (95% CI 0.85–1.02, I2 = 34.6%; P = 0.114) for the overweight group and to 1.40 (95% CI 1.17–1.67, I2 = 86.1%; P < 0.01) for the obese group. We have shown that obesity or underweight is associated with an increased risk of frailty in community-dwelling older adults.