Myasthenia gravis (MG) is a disease involving neuromuscular transmission that causes fatigue of skeletal muscles and fluctuating weakness. It has been shown that impairment of myogenic differentiation and myofiber maturation may be the underlying cause of MG. In this study, we detected the abnormal expression of circular RNA (circRNA) using next-generation sequencing in patients with MG. We then investigated the regulatory mechanism and the relationship among circRNA, microRNA, and messenger RNA using quantitative reverse-transcription polymerase chain reaction, bioinformatics analysis, and luciferase report analysis. The expression of inflammatory cytokines and regulatory T lymphocytes was shown to be increased. Circ-FBL was significantly increased in MG patients. Bioinformatics and luciferase report analyses confirmed that miR-133 and PAX7 were the downstream targets of circ-FBL. Overexpression of circ-FBL promoted myoblast proliferation by regulation of miR-133/PAX7. Taken together, our study showed that upregulation of circ-FBL promoted myogenic proliferation in patients with MG by regulating miR-133/PAX7.