[en] The aim of this work was to determine the background airborne radioactivity in the town of Natal, Brazil. Indoor radon concentrations were measured inside 24 buildings using solid state nuclear track detectors which were exposed for a period of about 180 days. The average indoor radon level resulted to be 15.4±10.6 Bq x m^-3. Measurements of gross α- and β-activities were performed at six different sites for airborne particulate samples collected over cellulose nitrate filters. Mean values of 0.15±0.06 mBq x m^-3 and 0.42±0.10 mBq x m^-3 were obtained for the gross α- and gross β-activity, respectively. (author)