Objective: The aim of this study is to determine the prevalence of idiopathic osteosclerosis (IO) in the mandible in an Iranian subpopulation using cone beam computed tomography (CBCT). Methods: This cross-sectional study was performed on all CBCT images obtained in 2010-2014 from the archive of Oral and Maxillofacial Radiology Department at Isfahan Dental School. Images were evaluated by two observers in identical room and monitoring conditions. IO was defined as homogenous radiopacities with no particular etiology, ranging from 2 mm to 2 cm in size. Demographic information of all patients, as well as the lesion’s number, location, border, shape, and association with adjacent teeth were recorded. Results: From 377 CBCT images, 43 images (11.4%) had at least one IO lesion. Two separate IO lesions were detected in six patients; therefore, 49 IO lesions were found in total. No gender differences were observed in IO prevalence (P = 0.806). Although most common in patients who were in their 30s, IO prevalence was not statistically different among age groups (P = 0.369). IO was most frequent in the molar region, with 63.2% of lesions. Conclusion: IO prevalence was 11.4% in the studied population and was not statistically different between age groups or sexes. Most lesions were found in the mandibular molar region.