Dependencies of dielectric properties on $MgTa_2O_6$, $MgNb_2O_6$, and $MgWO_4$ (Mg-based ceramics) fillers of the polystyrene (PS) matrix composites were investigated as a function of frequency. With increasing frequency from 1 GHz to 7.3 GHz, the dielectric constant (K) of the composites was not changed significantly, while the dielectric loss (tan${delta}$) of the composites was slightly decreased. The K, tan${delta}$, and temperature coefficient of resonant frequency (TCF) of the composites were dependent on the type and amount of ceramics at 11 GHz. Also, several theoretical models have been employed to predict the effective dielectric constant of the composites and the results were compared with experimental data. Typically, a K value of 6.67, tan${delta}$ of $0.56{ imes}10^{-3}$, and TCF of -4.99 $ppm/^{circ}C$ were obtained for the PS composites with 0.4 volume fraction of $MgNb_2O_6$ at 11 GHz.