By using the melt mixing method, polystyrene (PS), low-density polyethylene (LDPE), and a PS/LDPE blend have been prepared. Fly ash was used as filler embedded in the PS/LDPE blend to form composites. The dynamic mechanical analysis (DMA) showed that the storage modulus (E′) decreases as the temperature increases. E′ increases clearly with fly ash loading, and the maximum E′ value was found for the composite loaded with 30 % fly ash content. The mean-field theory developed by Kerner was used to predict the dynamic mechanical properties of the composites from their pure components. A good agreement was investigated between the deduced theoretical values via iteration method and the experimental results. The dielectric constant (ε′), dielectric loss, and dielectric loss tangent (tan δ) have been measured at different constant frequencies. The ε′ and tan δ commence to decrease by increasing the applied frequency.