Myositis ossificans is a rare cause of trismus. We present a case of pseudomalignant myositis ossificans involving medial pterygoid, lateral pterygoid, and temporalis muscles. Patient presented with gross limitation in mouth opening. There was no history of trauma. Computed tomography (CT) images revealed a bone density mass located in the region of medial and lateral pterygoid muscles on the right and temporalis muscle on the left. Magnetic resonance imaging (MRI) showed similar findings. Radiological diagnosis was pseudomalignant myositis ossificans. The masses were resected and histopathologic examination confirmed the above diagnosis. This report describes the characteristic CT and MRI features. The unique feature of this case is the absence of history of trauma with involvement of multiple masticatory muscles, which, to the best of our knowledge, has not been reported before.