Crystals of RbH(SO4)(0.81)(SeO4)(0.19) formulation are studied by H-1 NMR spectroscopy. The H-1 Line-shape, the line width and the T-1 and T-2 relaxation times are determined as a function of temperature. The activation energies deduced from the temperature dependence of line width and relaxation times are compared with the activation energy issued from conductivity measurements by impedance spectroscopy. The results obtained are discussed and supported by the help of the Ngai model.