This is a case of a 69-year-old male, with well-controlled rheumatoid arthritis and benign prostatic hyperplasia, who presented with fever and generalized weakness. He was found to have atrial fibrillation on his second emergency department visit and later diagnosed with human granulocytic anaplasmosis (HGA). Atrial fibrillation subsided with the commencement of HGA-specific treatment. This is the first case of HGA and atrial fibrillation reported in the English literature. It highlights the importance of being vigilant for unusual presentations of tick-borne diseases in the endemic areas.