Abstract: This study was designed to determine the season for the peak of WNV activity in a semi-arid zone Nigeria. A total of 973 sera from patients with febrile illness suspected of malaria/typhoid fever were used for the study. The sera were assessed for IgM and IgG antibodies to West Nile Virus (WNV) and Yellow Fever Virus (YFV) by IgM capture ELISA (MAC-ELISA). The IgM positive sera for WNV were also tested by Plaque Reduction Neutralization Test (PRNT) and RT-PCR. Twelve (1.2%) of the 973 sera tested had WNV IgM antibodies. Possible mixed infections of DEN-2 and WNV was observed in two samples. The prevalence of these antibodies during the cold harmattan period (IgM-2.9%) was significantly different from the dry (IgM-0.0%) and rainy season (0.1%). Overall, PRNT and ELISA results were in concordance The peak of WNV activity in the Semi arid Zone in Nigeria appeared to be November. A significant number of the patients tested (80.2%) had WNV IgG and the prevalence of WNV IgG was significantly different according to seasons. No YFV IgM was detected in 973 sera tested; nevertheless, a significant number of the patients (86.9%) had YFV IgG antibodies. Seasonal association with YF IgG antibody was observed. A positive correlation of seasons with incidence was found. To mitigate future impacts, both disease surveillance and control are necessary during the season with highest virus activity.