 This is a single-arm study. Key eligibility criteria include 1 newly diagnosed, diffuse large B-cell or follicular cell non-Hodgkins lymphoma; 2 negative test for hepatitis B surface antigen HBsAg and positive for antibody to hepatitis B core antigen anti-HBc; 3 adequate bone marrow, liver, and kidney function. All eligible patients will receive rituximab-CHOP cyclophosphamide, doxorubicin, vincristine, prednisolone chemotherapy according to current treatment guidelines. The primary endpoint of this study is the incidence of hepatitis B virus HBV reactivation, defined by a greater than 10-fold increase, compared with previous nadir levels, of HBV DNA during rituximab-CHOP chemotherapy and within 1 year after completion of the last course of rituximab-CHOP chemotherapy. Patients who have HBV reactivation during the study period will receive free entecavir treatment, one of the standard treatment for chronic hepatitis B, for 48 weeks. The secondary endpoints include the incidence of hepatitis flare, defined as a greater than 3 fold increase of serum alanine aminotransferase ALT level that exceeded 100 IUL, and the efficacy and safety of rituximab-CHOP chemotherapy. 