Bendamustine is one of the new key drugs for patients with indolent lymphoma. Bendamustine, together with rituximab, significantly improves the treatment outcomes of these patients. In addition, previous clinical studies have shown the complication rate of severe infection in bendamustine-containing regimens to be relatively low as compared to those of conventional chemotherapeutic regimens such as CHOP. However, some clinical case reports have raised the possibility that bendamustine may abrogate the immune responses of patients and trigger opportunistic infections including cytomegalovirus reactivation. Herein, we report three indolent lymphoma cases becoming positive on cytomegalovirus antigenemia assay during bendamustine monotherapy. All events occurred after more than three courses of treatment with bendamustine. One patient showed decreased CD4 positive T lymphocytes before the development of cytomegalovirus antigenemia. All three patients were successfully treated with valganciclovir. Although the precise risk is unknown, it should be noted that bendamustine can potentially cause reactivation of/infection with cytomegalovirus and physicians should pay attention to the possibility of this infection during treatment with bendamustine-containing regimens.