Radiofrequency coagulation was introduced to reduce the volume of masseter muscle. Radiofrequency procedure causes focal necrosis in masseter muscles, which leads to muscle hypoplasia and a slender lower face. We present a case of a 24-year-old woman who underwent radiofrequency coagulation to reduce masseter muscles. The patient experienced progressive erythematous swelling and noticed the mass around the right cheek 5 days after the procedure. On radiologic evaluation, a round cavity of 4-cm diameter containing air and fluid was observed. Incision and drainage was performed, and antibiotics were administrated intravenously. Blood-tinged purulent fluid was obtained, which was subsequently found to have a high amylase level. The swelling subsided, and there is no relapse up to 6 months after drainage. There are several complications of radiofrequency coagulation reported such as mucoserous fluid collections, late bleeding, infections, long-lasting pain, Stensen duct injury, facial nerve injuries, and limitation of temporomandibular joint movement. A well-designed operation plan and skilled technique are required to avoid these complications.