Accessory submandibular salivary gland (ASSG) is an extremely rare variation of the submandibular salivary gland. We reported a 65-year-old man with prostate cancer underwent Ga-PSMA PET/CT for active surveillance. The images showed abnormal PSMA uptake adjacent to the submandibular salivary gland without abnormal activity distribution in the rest regions of the body. The lesion density was similar to that of the submandibular salivary gland. Pathological biopsy confirmed that it was an ASSG. Our case illustrates that ASSG is an addition benign cause of extraprostatic uptake of PSMA.