Myositis ossificans is a condition characterized by ossification within a muscle. It is a rare and unusual pathologic entity that has defied medical efforts to establish a definite etiology, pathogenesis, and satisfactory treatment of the disease. The condition predominantly affects the flexor muscles of the upper limbs and thighs, but rarely the head and neck area. A 53-year-old male patient visited our medical institution complaining of trismus, defined as limited mouth opening. The patient had a history of trauma to the facial bones and the computed tomography scans revealed calcification in the left temporalis muscle. The patient underwent surgical removal of the calcified mass with bilateral coronoidectomy under general anesthesia. Mouth opening at the end of post-operative 2 months was 28 mm. His oral intake of food was satisfactory. Myositis ossificans of the temporalis muscle is a very rare case. Satisfactory outcome was obtained by combining surgical excision of the affected muscle, coronoidectomy, and detachment of the insertion site of the ossified muscle.