Twisted nematic liquid crystal display (TN-LCD) devices, composed of nematic liquid crystal (NLC), doped with silver (Ag) nanoparticles, which are protected with the same NLC molecules of 5CB (Merck, K-15), show electrooptic characteristics that are featured by a frequency modulation and fast response. This device is called FM-TN-LCD. In this paper, we report that the frequency range in the FM-TN-LCD spreading from 40 Hz to an upper limit 2 kHz correlates with that of the dielectric dispersion of the sample cell, which is expressed analytically by the Maxwell–Wagner theory on the heterogeneous dielectric medium, where the dielectric relaxation frequency, and thus the dielectric relaxation time, are primarily governed by the electrical conductivity of the doped Ag nanoparticles.