We have studied the transient response of some capacitor systems during the charging process to a step function voltage. The dielectric materials used were MOR type zeolites showing 80 % of crystalline phase, as determined by X-ray diffraction (XRD) Using the Fourier integral transform and the Kramers-Kronig relations we have obtained the real and imaginary part of the permittivity. In some of these spectra a negative capacity effect has been observed. This uncommon effect is interpreted through the "universal response law" for dielectrics relaxation in solids. Based on the strong low frequency dispersion mechanism a phenomenological approach is proposed to explain these results taking into account the physical properties and structure of the zeolites.