HBcAg
（重定向自Hepatitis B core antigen）
![A simplified drawing of the HBV particle and surface antigen. Purple = Lipid Envelope, Red = Nucleocapsid Core (Note: This drawing is slightly misleading in that the nucleocapsid core is a single entity even though it is depicted as a light blue icosahedral line shape and a red ring of circles).](/Images/godic/202501/17/Hepatitis_B_virus_v2.svg4223.png")
![The genome organisation of HBV. The genes overlap. (ORF Core, at bottom left, encodes HBcAg.](/Images/godic/202501/17/HBV_Genome.svg4223.png")
HBcAg (core antigen) is a hepatitis B viral protein. It is an indicator of active viral replication; this means the person infected with Hepatitis B can likely transmit the virus on to another person (i.e. the person is infectious).