This study reports the aerodynamic properties of ground biochar particles produced from the slow pyrolysis of mallee biomass at 400 °C, considering grinding times from 10 s to 16 min. The data show that extensive grinding (e.g., ≥1 min) substantially increases the amounts of particulate matter with an aerodynamic diameter of <10 μm (PM10) and <2.5 μm (PM2.5) in the ground biochars. Whereas the aerodynamic particle size distribution (PSD) of PM10 in biochar after grinding for 10 s shows no obvious peak, a bimodal PSD is observed for PM10 in the biochars after grinding for 1–16 min. The results suggest that care must be taken during biochar grinding to minimize the PM10 and PM2.5 produced. PM10 and PM2.5 in a biochar should also be quantified to assess environmental risks during biochar transport and applications.