The novel coronavirus disease 2019 (COVID-19) clinically manifests as respiratory and gastrointestinal presentations, most commonly vomiting, diarrhea, and abdominal pain. Although the impaired liver function is prevalent in COVID-19, it is poorly understood. We report the first case of hepatitis B virus (HBV) reactivation caused by COVID-19 in a young adult with altered mental status and severe transaminitis. The patient was asymptomatic, hypothermic, his skin was jaundiced with the icteric sclera, with very high levels of aspartate aminotransferase (AST; 4,933 U/L), alanine aminotransferase (ALT; 4,758 U/L), and total bilirubin (183.9 mmol/L) levels. It is warranted that patients with abnormal liver functions tend to have an increased risk of COVID-19. Thus, increased attention should be paid to the care of patients with abnormal liver functions, and testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA is warranted in the COVID era.