Severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) causing a human pandemic disease named COVID-19 has become a major global health concern. Iran as one of the most affected countries needs unprecedented effort for monitoring and evaluation of COVID-19. To determine the seroprevalance of COVID-19 in Semnan province North-East of Iran. Six hundred people were randomly selected using the "SIB data-base". From 1 to 30 June, 2020, 153 participants of Semnan population were enrolled. Blood, nasopharyngeal and oropharyngeal samples were obtained. Prevalence of IgM and IgG antibodies were ascertained using ELISA and Real-Time PCR was conducted to evaluate viral load. Estimates of prevalence were standardized by age and sex, based on the 2015 national census of Semnan province. Seroprevalence showed no difference between females and males and no significant association between age and seropositivity. Among total participants, the age and sex adjusted prevalence of SARS-CoV2 infection was 19.3% (95% CI, 14.0-26.7 per 100 persons). Approximately 10% of participants had detectable antibodies but showed a negative-PCR result. However, approximately 80% of participants did not show an evidence of infection. The majority of the population in Semnan province has no detectable antibodies to SARS-CoV-2. Therefore, Semnan is considered a SARS-CoV-2 susceptible area. These results emphasize the need for maintaining public health measures to tackle the new epidemic wave.