Macrophage activation syndrome (MAS) is a rare complication in systemic lupus erythematosus (SLE) that can be triggered by infections. Due to the fact that MAS may mimic clinical features of underlying rheumatic disease, or be confused with an infectious complication, its detection can prove challenging. This is particularly true when there is an unknown/undiagnosed disease; and could turn into an even greater challenge if MAS and SLE are combined with a viral infection. A—i4-year—old female came to the hospital with an ongoing fever for 2 weeks and a painful facial skin rash. Hepatomegaly, pancytopenia, increased aspartate aminotransferase, elevated serum ferritin and lactate dehydrogenase were reported. No hemophagocytic infiltration of bone marrow was reported. The patient was suspected for hemophagocytic lymphohistiocytosis. Her skin rashes were eczema herpeticum, which is usually associated with immune compromised conditions. With the history of oral ulcers and malar rash, positive ANA and low C3, C4 and the evidence of hemolytic anemia, she was diagnosed as SLE. According to the diagnostic guideline for MAS in SLE, she was diagnosed MAS as well, activated by acute HSV infection. After administering steroids and antiviral agent, the fever and skin rash disappeared, and the abnormal laboratory findings normalized. Therefore, we are reporting a rare case of MAS triggered by acute HSV infection as the first manifestation of SLE.