Residual softwood sawdust (RSS) was added to polystyrene (PS) that has molecular weight 280000 g/mol. The PS composite was prepared by melt mixing technique. The dynamic mechanical tests are carried out using ARES-rheometer (Rheometric Scientific, USA) in the dynamic mode and parallel plate geometry with diameter 25 mm. The measurements were performed at temperatures ranging from 140 to 240°C and frequencies varied from 0.1 to 100 rad/s at strain 1% and gap setting 2 mm. The dynamic mechanical properties in terms of complex modulus, G*, torque, compliance moduli, loss tangent and complex viscosity has been studied for fiber-filled PS composite. The viscoelastic properties of the filled and unfilled systems have been compared. These properties are found to be improved by the addition of RSS. The dynamic mechanical moduli and viscosity were found to rise with fiber loading.