Herpes simplex encephalitis (HSE) and anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis are associated entities. On the contrary, although both are autoimmune diseases, the association of neuromyelitis optica spectrum disorder (NMOSD) and anti-NMDAR encephalitis is not well explained. Herein, we present consecutively developed post-herpetic anti-NMDAR encephalitis in a patient with the coexistence of NMOSD and Sjogren syndrome. In our patient evaluation with MRI and clinical findings, the diagnosis of HSE after immunosuppressive drug application for NMOSD was made. Whereupon, HSE triggered NMDAR encephalitis. Many authors demonstrated the induction of anti-NMDAR encephalitis over herpes encephalitis with the presence of movement disorders, psychiatric manifestations, and cognitive dysfunction. In our patient, without biphasic disease activity; the persistence of symptoms, new MRI findings, and the positivity of anti-NMDAR antibody confirmed the anti-NMDAR encephalitis diagnosis. Our patient is a representative case mentioning the importance of close follow-up of a patient in neuroimmunology.