Pure trigeminal motor neuropathy is a rare clinical manifestation, and its etiology remains obscure. Here, we report the case of a 67-year-old woman who presented with jaw deviation to the right. Neurological examination revealed atrophy of the right temporal and masseter muscles and jaw deviation to the right. Absence of other cranial nerve abnormalities, such as loss of sensation in the trigeminal nerve territory, suggested involvement of only the motor component of the right mandibular nerve. Results of laboratory tests, including hematologic, serologic, and biochemical analysis, were unremarkable, except for the finding of lymphocytic pleocytosis in the cerebrospinal fluid on symptom onset. Brain MRI revealed no abnormality in the brainstem or trigeminal nerve. Electromyography indicated chronic denervation in the right temporal muscle. A few days before the occurrence of the neurological signs, the patient had experienced flu-like symptoms; this suggests that post-infection neuropathy may be a possible cause of the right motor trigeminal neuropathy observed in our case.