Kikuchi Fujimoto Disease (KFD), also known as necrotic histiocystic lymphadenitis, is a condition with unknown etiology. Probably, infectious, viral, and also autoimmune etiologies, especially lupus erythematosus, contribute to this disorder. The common signs are lymphadenopathy along with fever and leukopenia. Our case was a13-year-old boy with fever of unknown origin. He underwent ordinary fever of unknow origin (FUO) investigations and the only positive finding on his examination was lymphadenopathic fever of posterior cervical chain. The results of primary tests and also cultures of blood and urine samples did not have any specific contribution to diagnosis of infectious causes. Besides, bone marrow aspiration and biopsy led to the exclusion of chances of lymphoma or other malignancies. Finally, diagnosis of KFD was confirmed by the use of dissection of cervical lymph nodes and also via immunohistochemical tests and simultaneous positive antinuclear antibody (ANA). Hence, the patient was put on suitable medical treatment for lupus. Given the rare demonstrations of this case, i.e., the male sex and fever of unknown origin, and also the positive ANA despite clear clinical symptoms of lupus, this case was presented to provide both proper education and make a faster and more appropriate diagnosis.