The mental nerve is a sensory nerve which traverses through mental foramen to innervate the lower lip, chin skin and the mandibular labial gingiva. Interestingly, it's variant such as the accessory mental foramen (AMF) was described as an unusual finding in the recent literature. Hereby, we reported a patient who was operated to treat the mandibular bisphosphonate-related osteonecrosis of the jaw (BRONJ) lesion. Intraoperatively, an accessory mental foramen was detected posterior to the main foramen and nerve, on the right side of the mandible. This case report highlighted the necessity for proper radiological and clinical evaluation of mental foramina in order to avoid nerve injury and postoperative paresthesia. The review of the literature and the clinical findings were also discussed in this article.