Hepatitis B is one of the most frequent post-transfusion infections. Occult hepatitis B infection (OBI) is a form of hepatitis B infection in which, despite the presence of HBVDNA in the serum and hepatocytes of the carrier, HBsAg is absent. In addition to the risk of transmission through the transfusion of infected blood, reactivation of hepatitis B in OBI patients and recipients of their blood can lead to cirrhosis, hepatic cancer, and reactivation of viral replication in the carrier. Therefore, effective assays to assess and screen for OBI in blood donors are of paramount importance and require urgent attention. Recently, several investigations in various regions of Iran have reported OBI in blood donors. In response, there has been a drive to apply more specific, sensitive, and accurate methods for the detection of HBV, which should become an obligatory screening process for all blood transfusion services. In this review, we address the progression of occult hepatitis B and the common problems associated with occult hepatitis B worldwide. Finally, we reflect on the research and screening that is being performed in Iran to deal with this problem.