In this study we present the particle number size distribution (diameter 0.3–10 µm with 1-minute time resolution) inside four offices (naturally ventilated) inside two university buildings. Each office had a typical environment in terms of occupancy and furniture. We focused on the differences between workdays and weekends in terms of particle number (PN) and particle mass (PM, assuming spherical particles with unit density) concentrations. Moreover, we illustrated the effect of workers’ activity (occupancy, smoking, etc.). We also applied a simple indoor aerosol model to estimate the fate (gravitational settling and exfiltration) and source strength of aerosol particles within the measured particle size range. During workdays, the highest measured 24-hour average PM10–1 in the occupied office was 41.5 µg m–3 (PN10–1 = 2.2 cm–3) compared to 9.0 µg m–3 (PN10–1 = 1.2 cm–3) in the unoccupied offices. The ventilation rate of the offices that were opposite to each other was about 0.15 h–1 whereas it was 0.28–0.38 h–1 for the other offices, which were a bit distant from each other. The gravitational settling analysis suggested that a suitable particle density (ρp) could be ~1.7 g cm–3 with a shape factor χ ~1.57, which is similar to mineral dust particles. The gravitational settling rate of particles around 2 µm in diameter was about 0.3 h–1. The source strength of indoor dust particles was higher in the occupied and carpeted offices (re-suspension emission rate as high as 235 µg m–3 h–1) in comparison to unoccupied and uncarpeted offices (75 µg m–3 h–1). This study provided us with an insight about the effect of occupancy and carpet use on the dynamic behavior (fate and re-suspension) of dust particles inside university office buildings located in semi-arid regions.