In this study, exposure to secondhand smoke (SHS) was evaluated in commercial personal computer (PC) rooms with different separation types of non-smoking areas. The particulate matter less than 2.5 ${mu}m$ ($PM_{2.5}$) level was simultaneously measured by aerosol spectrometers in the non-smoking and smoking areas of these commercial PC rooms. Average $PM_{2.5}$ concentrations in non-smoking and smoking areas were $75;{mu}g/m^3$ and $136;{mu}g/m^3$, respectively. Although the $PM_{2.5}$ concentrations in non-smoking areas were significantly less than those in smoking areas (p<0.01), the levels still exceeded the US National Ambient Air Quality Standard of $35;{mu}g/m^3$. Average $PM_{2.5}$ concentrations in non-smoking areas were not significantly different with regard to area separation type, with $73;{mu}g/m^3$ in the no-wall type, $83;{mu}g/m^3$ in the wall-type, and $39;{mu}g/m^3$ in the separated-floor-type areas (p>0.1). Separation of the non-smoking area thus did not eliminate SHS exposure in commercial PC rooms, regardless of the type of area separation. This study demonstrates that simple separation of non-smoking areas in commercial PC rooms does not protect users from SHS.