Indoor air quality may be compromised by elevated radon levels, a naturally occurring radioactive gas. Prolonged exposure to increased radon levels can adversely affect human health. This paper presents the results of indoor radon activity concentration measurements conducted at 20 locations using a passive method. CR-39-based radon detectors were deployed over three different exposure periods, from January to April. The aim of the study was to compare and analyse average indoor radon activity concentrations obtained over different detector exposure periods, and to determine whether reliable information on indoor air quality can be obtained using shorter exposure durations. The measured indoor radon activity concentrations ranged from 6.0 to 727 Bq/m3, 10.1 to 561 Bq/m3, and 15.1 to 480 Bq/m3 for the three-month, two-month, and one-month exposure periods, respectively. Comparative analysis of the results showed that the mean ratio of radon activity concentrations for one-month to two-month, two-month to three-month and one-month to two-month exposure periods were 1.24, 1.57 and 1.85, respectively. To establish the relationship between radon activity concentrations obtained for different exposure periods, linear regression analysis was performed. The analysis of the estimated relative percentage differences showed that the results for different exposure periods agreed within ±20% at approximately 53% of the locations.