HBV infection is a major global health concern, leading to numerous HBV-related deaths. Due to the lack of curative or eradicative treatments for HBV, a large number of individuals in the general population are at risk of HBV reactivation. The increasing application of ICIs for treating various malignancies has raised concerns about HBV reactivation caused by these therapies. HBV reactivation complicates the treatments, leading to the interruption or modification of therapeutic regimens, which presents a considerable challenge. In this review, we summarize relevant researches on the definition, prevalence, and pathogenesis of HBV reactivation. Furthermore, we discuss the risks and mechanism of HBV reactivation during ICIs treatment, outline management strategies for HBV reactivation, and provide recommendations for assessing and monitoring HBV status during the treatment process.