The neurologic complications associated with the coronavirus disease 2019 (COVID-19) is becoming more prevalent in children after the appearance of the Omicron strain. An association between COVID-19 and posterior reversible encephalopathy (PRES) has been consistently reported in adults, but little information is available in the pediatric age group. There are only few case reports of COVID-19-related PRES in children, and all of these patients were either on some type of immunomodulatory medications or whose general condition was severe. The present case, a 9-year-old Japanese boy, who had no fever but vomited several times from days 1-4 of a COVID-19 infection had an afebrile seizure on the 8th day of his illness. The patient had no history of hypertension, and had not previously been administered any immunosuppressive drugs before or during the period of his COVID-19 infection. On admission, his physical findings were unremarkable, except for a high blood pressure. The results obtained by brain computed tomography and magnetic resonance imaging were consistent with PRES. The patient recovered with no sequelae after treatment with antihypertensive drugs. Further investigations did not suggest any underlying disease that could have caused the transient hypertension. Although PRES is relatively rare in children, pediatricians should keep in mind that this syndrome can be complicated, even in children with mild COVID-19 infections.