We herein report a 72-year-old woman with rheumatoid vasculitis who exhibited a depressed level of consciousness after receiving the first dose of the Pfizer-BioNTech mRNA BNT162b COVID-19 vaccine and was diagnosed with meningoencephalitis. Although there was no confirmatory examination, the diagnosis was based on magnetic resonance imaging (MRI) findings and etiological assessments, including microbiological and autoimmune investigations. Both intravenous steroid pulse and gammaglobulin therapies alleviated the patient's symptoms, and the MRI findings improved. Although the efficacy of COVID-19 vaccination has been widely accepted, such neurologic complications might occur in patients with rheumatoid diseases or vasculitis syndromes.