With increasing temperature, the NMR line of nuclei in the spin glass region of random mixture Co 1- x Mn x Cl 2 ·2H 2 O becomes gradually sharp and symmetric, and disappears at the transition temperature T RSG from the reentrant spin glass to the antiferromagnetic phase. This phenomenon shows the change in the randomness of frozen spins and is analysed by considering the temperature dependence of the probabilities for ferro- or antiferromagnetic configurations. Based on the analysis of the observed spectra, we conclude that the randomness of the frozen spins decreases with increasing temperature.