This is a single-center, open-label study of ARC-520 in combination with entecavir or tenofovir administered to patients with immune active chronic HBV infection. An iterative trial design is anticipated with potential inclusion of additional cohorts with anticipated enrollment of up to 60 patients. Patients who have signed a Human Research Ethics Committee approved informed consent, and have met all of the protocol eligibility criteria will continue receiving daily oral entecavir (0.5-1.0 mg/day) or daily oral tenofovir (300 mg/day) and a single IV injection of ARC-520. If a serious adverse event (SAE) deemed possibly or probably related to study drug should occur at any point during the study, any further dosing will be put on hold pending a complete review of safety data by the sponsor and the Principal Investigator. Patients will undergo the following evaluations at regular intervals during the study: medical history, physical examinations, vital sign measurements (blood pressure, heart rate, respiratory rate, and temperature), weight, AEs, 12-lead ECGs, concomitant medication, blood sample collection for hematology, coagulation, chemistry, PK and exploratory PD measures, HBV virology. Patients will be monitored for a total of 12 weeks. Clinically significant changes including AEs will be followed until resolution, until the condition stabilizes, until the event is otherwise explained, or until the patient is lost to follow-up.