We have studied a system composed of a hydrophobic aerosil (R812) dispersed in the liquid crystal 4-n-octyl-4'-cyanobiphenyl (8CB) using the spin probe electron spin resonance (ESR) technique, and in particular, we have determined, for different aerosil concentrations, the temperature dependence of the orientational order parameter, , and the rotational diffusion coefficient, D-perpendicular to, of the probe 5-doxyl stearic acid in the ordered and isotropic phases of the system. We have found that increasing the silica concentration up to 10 wt % does not significantly change the transition temperatures of the system. The probe order parameter is instead depressed, and we found that the beta exponent of an empirical Haller-type equation, used to fit its temperature dependence, changes roughly linearly with the aerosil concentration. The concentration effect on the probe dynamics is relatively small in the isotropic phase, where the D-perpendicular to temperature dependence is well fitted for all of the systems with an Arrhenius-type equation. In the nematic phase, the dynamical behavior is more complex: we found that, while local probe motion is still rather fast even when the macroscopic behavior is gellike, the temperature dependence of D-perpendicular to is still of Arrhenius-type up to 3 wt % aerosil concentration but it becomes of Vogel-Fulcher-Tammann-type for the 10 wt % R812 system.