A Study of Orally Administered JNJ-56136379 to Evaluate Safety, Tolerability and Pharmacokinetics After Single Ascending Doses and One Multiple Dose Regimen in Healthy Participants (Part I), and After Multiple Dose Regimens in Participants With Chronic Hepatitis B (Part II)

The purpose of this study is to evaluate pharmacokinetics and safety data including serious and other adverse events, physical examinations, vital signs, 12-lead electrocardiograms (ECGs) and clinical laboratory results (including biochemistry, hematology, and urine).

Part 1: This is a first-in-human (FIH), double-blind (neither the researchers nor the participants know what treatment the participant is receiving), randomized (study medication assigned to participants by chance), placebo-controlled (an inactive substance; a pretend treatment \[with no drug in it\] that is compared in a clinical trial with a drug to test if the drug has a real effect) study. Part 1 includes healthy adult participants, divided into 3 panels (Panel 1, 2 and 3) and in Part 2 adult Chronic Hepatitis B Participants will be included, in Sessions VIII to XI and Optional Sessions A-B-C (Panel 4). The study will consists of screening phase (part 1: \[less than or equal to \<=28 days before the first intake of study drug; part 2: \[\<=56 to greater than or equal to {\>=} 20 days before the first intake of study drug), Treatment Phase (multiple dose phase in part 1: Day -1 up to 12 or 19 days; part 2: up to 4 weeks) and Follow up Phase (part 1: 30-35 days after last study drug intake or after dropout; part 2: up to week 8 after actual end of study drug treatment). Participants' safety will be evaluated throughout the study.

Eligibility Criteria:
Inclusion Criteria:

* For Part II, a female participant must be either of a) Non-childbearing potential defined as: 1) Postmenopausal: A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high follicle stimulating hormone (FSH) level (greater than (\>)40 international unit per milliliter (IU/L) or milli-international units per milliliter (mIU/mL) in the postmenopausal range may be used to confirm a postmenopausal state in women not using hormonal contraception or hormonal replacement therapy, however in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient, or 2) Permanently sterile: Permanent sterilization methods include hysterectomy, bilateral salpingectomy, bilateral tubal occlusion/ligation procedures, and bilateral oophorectomy, or b) Childbearing potential and practicing sexual abstinence or a highly effective method of contraception from screening onwards and agree to continue to use the same method of contraception throughout study treatment and for at least 90 days after the last dose of study drug (or longer, if dictated by local regulation)
* Female participants should have a negative serum pregnancy test at screening
* Healthy Participants: Participants must have a body mass index (BMI; weight in kg divided by the square of height in meters) of 18.0 to 30.0 kilogram per square meter (kg/m2), extremes included
* Chronic Hepatitis B Participants: Participants must have lack of advanced liver disease, ie, either: Metavir F0-F2 (or comparable histologic scoring system) as determined on a liver biopsy within one year of the screening visit; a result based on specific radiologic liver disease staging modalities (eg, Fibroscan, AFRI, magnetic resonance imaging \[MRI\]-Elastography) compatible with Metavir F0-F2 within 6 months of the screening visit
* Chronic Hepatitis B Participants: Participants must have HBV DNA of greater than or equal \[\>=\] 2,000 international unit per milliliter (IU/mL) at screening
* Chronic Hepatitis B Participants: Participants must be aged between 18 years to 65 years, have a body mass index (BMI; weight in kg divided by the square of height in meters) of 18.0 to 35.0 kilogram per square meter (kg/m\^2), extremes included

Exclusion Criteria:

* Healthy Participants: Participants with a past history of cardiac arrhythmias (example, extrasystolic, tachycardia at rest), history of risk factors for Torsade de Pointes syndrome (eg, hypokalemia, family history of long QT Syndrome)
* Healthy Participants: Female participants who are breastfeeding at screening
* Healthy Participants: Participants with current human immunodeficiency virus type 1 (HIV-1) or HIV-2 infection (confirmed by antibodies) at screening
* Chronic Hepatitis B Participants: Participants with current HCV infection (confirmed by HCV antibody or HCV RNA) or hepatitis delta virus (HDV) infection (confirmed by HDV antibody) at screening
* Chronic Hepatitis B Participants: Participants with positivity of anti-HBs antibodies
* Chronic Hepatitis B Participants: Participants with a past history of cardiac arrhythmias (eg, extrasystolic, tachycardia at rest), history of risk factors for Torsade de Pointes syndrome (eg, hypokalemia, family history of long QT Syndrome)
* Chronic Hepatitis B Participants: Female participants who are breastfeeding at screening