Background: One of the most important natural sources of human exposure is inhalation of radon radioactive gas and its decay products in homes and at workplaces. According to the World Health Organization, radon is the second leading cause of lung cancer. This study is the first survey of indoor radon concentration in dwellings of the Aleshtar city (west of Iran). Materials and methods: In this work, radon concentrations were measured in 24 dwellings by using a passive method known as Alpha Track Detectors (ATDs) with CR-39 polycarbonate film for three months during the year 2016. In addition, the annual effective dose due to radon exposure was estimated for residents. Results: The indoor radon concentration ranged from 1.01 to 206.53 Bq/m³ with an average value of 55.19 Bq/m³ (CI (Confidence Interval) 95%: 31.46 - 78.92), and the average annual effective dose to the population in Aleshtar was estimated to be 1.39 mSv/y. According to the result of this study, there was a significant difference between apartment buildings and villas as well as between different floors in terms of the average radon concentration. Conclusion: It was found that radon concentration in 20.8% of dwellings was higher than the reference levels recommended by the World Health Organization (100 Bq/m³).