A 55-year-old woman underwent FDG PET/CT to detect possible multiple myeloma due to IgM κ paraproteinemia. FDG PET/CT showed a focal intense activity with SUVmax of 21.3 in her anterior tongue, suspicious for malignancy. MRI and physical examination of the tongue were normal. On further inquiry, the patient reported she had a habit of licking her anterior mandibular teeth and licked her teeth repeatedly before and after injection of FDG. Consequently, the tongue activity was interpreted as physiological tongue muscle activity due to repeated tooth-licking.