Infectious mononucleosis is caused by the Epstein-Barr virus (EBV) and may rarely result in neurological complications. Here, we report a case of brachial neuritis following EBV-induced infectious mononucleosis. A 28-year-old female presented with a sore throat and mild fever and was diagnosed with infectious mononucleosis. At that time, she also experienced bilateral shoulder pain and muscle weakness, for which she received intravenous steroid pulse therapy followed by oral steroids. Despite treatment, she continued to exhibit persistent muscle weakness. An electrodiagnostic study later revealed axonal neuropathy with signs of regeneration in both the axillary and suprascapular nerves, consistent with brachial neuritis. The patient was instructed in exercises to strengthen her shoulder muscles and maintain joint range of motion during outpatient visits, leading to an improvement in her symptoms.