Objective: To determine the seroprevalance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in the general population of Mazandaran province in Iran and to estimate the percentage of asymptomatic, mild, and severe infections. Methods: We chose 1588 inhabitants of Mazandaran province with cluster sampling. We measured their SARS-CoV-2 immunoglobulin M (IgM) and immunoglobulin G (IgG) serum levels. Demographics, risk factors, and symptoms were collected. The seroprevalence of SARS-CoV-2 was calculated by age and city and the World Health Organization (WHO) protocol and further stratified by demographic variables and risk factors. Finally, we identified the symptoms and factors related to COVID-19 with logistic regression. Results: Two hundred subjects (12.59％) were tested positive for either IgG or IgM. Until May 23, 2020, the prevalence of COVID-19 was 15.26％ (95％ CI: 12.97％-17.79％) based on direct standardization and WHO's standardized age groups. Based on multivariate logistic regression, the incidence of getting an infection increased by an average of 11.6％ for every 10-year increase in age (OR=1.116, 95％ CI: 1.008-1.236, P=0.035). Furthermore, those in contact with COVID-19 patients had a 66.1％ higher risk of developing the disease (OR=1.661, 95％ CI: 1.104-2.497, P=0.015). In addition, the chance of getting SARS-CoV-2 infection was almost four times higher in people who had consulted a doctor during the pandemic than those who had not (OR=3.942, 95％ CI: 2.813-5.524, P<0.001). Conclusions: The prevalence of COVID-19 in Mazandaran province could be higher than the officially reported statistics basedon diagnostic tests and clinical cases. There seems to be more asymptomatic or mild symptom cases than what was previously reported.