Using a tight binding model, we have investigated charge transport in model DNA sequences under external ac bias. The numerical results of emittance for several model DNA sequences are found to be well described by an analytical formula, especially when the dynamic response is inductivelike. This formula can be understood from general considerations of scattering matrix theory. The temperature dependence of emittance is also studied numerically within the tight binding model, and dynamic response of the model DNA sequences can change from inductivelike to capacitivelike as temperature is varied.