We herein report a case of myelin oligodendrocyte glycoprotein-antibody-associated disorder (MOG-AD) presenting with corticomeningeal encephalitis. The patient exhibited oral ulceration, a mild impairment of consciousness, fever, nausea, nuchal rigidity, positivity for human leukocyte antigen type B51, and neutrophil-dominant pleocytosis and interleukin-6 level in cerebrospinal fluid (CSF). Magnetic resonance imaging (MRI) revealed a right temporal lesion with leptomeningeal gadolinium enhancement. The initial diagnosis was neuro-Behçet's disease presenting with meningoencephalitis; however, a cell-based assay detected anti-MOG antibody in the serum and CSF and the patient also experienced bilateral optic neuritis. After administering steroid therapy, his neurologic symptoms and CSF abnormalities improved along with the disappearance of gadolinium enhancement and the lesion on MRI. This case suggests that MOG-AD may present with corticomeningeal encephalitis prior to the onset of optic neuritis.