Through the measurement of dielectric dispersion as a function of frequency (100 Hz less than or equal to f less than or equal to 1 MHz), we investigated the trapping dielectric relaxation of r.f.-sputtered (Ba0.5Sr0.5)TiO3 film and proposed an equivalent circuit on the basis of the admittance and capacitance spectra. Admittance spectral studies in the temperature range of 200-420 K revealed the existence of a trap level. The trap, located at 0.05 eV, is envisaged to be responsible for the origin of dielectric relaxation and carrier concentration. The equivalent circuit, consisting of a series trapping resistance and capacitance combination in parallel with leakage resistance and high frequency limit capacitance, is adopted to explain satisfactorily the AC response and to identify the contribution of the shallow trap on the electrical properties of BST thin film.