Reactivation of hepatitis B virus (HBV) is not infrequently reported in patients with rheumatologic diseases treated with biologic disease modify anti-rheumatic drugs (DMARDs) such as a tumor necrosis factor-alpha inhibitor or a B cell depleting molecule. HBV reactivation is reported not only in patients with chronic hepatitis B but also in cases with resolved HBV where HBsAg is negative and anti-HBc positive. Studies suggest that with treatment using biologic DMARDs, the risk of HBV reactivation increases when HBsAg is positive independent of HBV DNA replication status, and in those with anti-HBc positive and serum HBV DNA positive. Therefore, testing for HBsAg as well as anti-HBc is important before initiating treatment with a biologic DMARD. In addition, evaluation of serum HBV DNA may be required when either HBsAg or anti-HBc turns out to be positive. Although series of reports suggest that prophylactic antiviral therapy in patients with higher risk of HBV reactivation would diminish morbidity and mortality from hepatic cause, solid guidelines pertaining to when to initiate and terminate HBV antiviral therapy and which agent should be used should be provided in the future.