Q fever is a disease caused by Coxiella burnetii, which infects both humans and certain animals, and is considered a public health problem. There is a lack of information on its status in most parts of Iran, including the northwestern area, which is one of the main centers of animal husbandry in Iran. This study was carried out to evaluate the seroprevalence of Q fever among sheep in the province of Ardabil in northwestern Iran. In all, 253 sheep samples were collected from different regions (north, central, and south) of Ardabil Province. Sera were tested by a CHEKIT Q fever enzyme-linked immunosorbent assay (ELISA) kit for detection of C. burnetii immunoglobulin G (IgG). A total of 33.6% of sheep sera and 87.50% of herds were positive for C. burnetii IgG. There was a significant difference between the regions studied (p<0.001) and the highest and the lowest rate of seroprevalence were seen in the south (58.6%) and central (23.3%) regions, respectively. Most of the seropositive cases were observed in 3- to 4-year-old the sheep (46.1%). There was no relationship between gender and the seroprevalence rate. Although this study was the first survey of Q fever in northwestern Iran, the high seroprevalence rate indicates that further attention should be paid to this disease in this region of the country.