The study will be conducted in 2 parts: dose escalation (Part 1) and dose expansion (Part 2). It will evaluate safety, tolerability, pharmacokinetics and preliminary antitumor activity of JNJ-64007957 administered to adult participants with relapsed or refractory multiple myeloma. The overall safety of the study drug will be assessed by physical examinations, Eastern Cooperative Oncology Group performance status, laboratory tests, vital signs, electrocardiograms, adverse event monitoring, and concomitant medication usage. Disease evaluations will include peripheral blood and bone marrow assessments at screening (performed within 28 days) and to confirm stringent complete response (sCR), complete response (CR), or relapse from CR. The end of study (study completion) is defined as the last study assessment for the last participant on study.