Radon-releasing mattresses were found to be manufactured using radium or thorium containing monazite, and a survey by the Korean Nuclear Safety and Security Commission found that some of these products exceeded radiation safety standards. Therefore, this study evaluates the radon distribution resulting from the radon released by such mattresses. For this purpose, Ansys Fluent computational fluid dynamics (CFD) codes were used to analyze the radon distribution in a general living space and to assess the radon exposure of residents. Drawings from the Korea Land and Housing Corporation were analyzed to determine the layout and geometry of a general residential space. The CFD simulation results were used to analyze the radon distribution in this space in terms of the ventilation direction and the distance from the source. The dose was evaluated to determine its radiation safety, and it was found to be less than 0.101 mSv/year; this value is below the International Commission on Radiological Protection’s recommendation of 10 mSv/year and the dose limit of 1 mSv/year for processed products in South Korea. The proposed method could be used to evaluate radon exposure in different environments to improve the safety of residents.