Ac conductivity measurements have been performed on the superionic glassy system (AgI)(x)(AgPO3)(1-x). It is found that there are two contributions to the ac conductivity : one, dominant at high temperatures/low frequencies, is characterised by a sublinear frequency exponent of the conductivity, s(1) similar or equal to 0.5, and the conductivity is thermally activated, with an activation energy smaller than, but comparable to, that of the dc conductivity; the second, dominant at low temperatures/high frequencies, is characterised by a superlinear frequency exponent, s(2) similar or equal to 1.2, and the conductivity is also thermally activated, but the activation energy is an order of magnitude smaller. The former behaviour is interpreted in terms of the diffusion-controlled relaxation model, and the latter in terms of local ionic hopping motion within a double-well potential with an exponentially decreasing distribution of barrier heights.