Epstein-Barr virus (EBV) is closely associated with several lymphomas, such as Burkitt lymphoma, natural killer/T-cell lymphoma, peripheral T-cell lymphoma, and Hodgkin's lymphoma; however, whether EBV is implicated in mantle cell lymphoma (MCL) has not been established. We report the case of an adult with recurrent infectious mononucleosis (IM)-like symptoms who developed an EBV-positive blastoid variant of MCL. A 54-year-old Japanese man presented with fever, swelling of the oral mucosa and tongue, dispersed pulmonary infiltrations, systemic lymphadenopathy, and splenomegaly. He had a history of recurrent IM-like symptoms (prolonged fever and cervical lymphadenopathy) for at least 1 year. MCL was diagnosed by biopsy of the cervical lymph node. The anti-EBV antibody titer indicated a reactivation of chronic infection with this virus. EBV was detected in most of the lymphoma cells and in the peripheral blood. EBV might have played some role in the tumorigenesis of blastoid MCL.