The magnetic viscosity of the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys were investigated, and the coercivity mechanism was discussed. The results show that the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys present hard magnetic behavior at room temperature. The intrinsic coercivity of the bulk amorphous decreases with increasing of the Pr addition from 0at% to 15at%. A single sharp and narrow peak close to the coercivity appears in the irreversible susceptibility (χirr) curve for each alloy. The addition of Pr has little influence on the magnetic viscosity of the alloys. With the substitution of Pr for Nd, the fluctuation field Hf decreases from 11.1 mT to 9.9 mT, and the activation volume Va increases from 2.6×10-18 cm3 to 2.9×10-18 cm3, which leads to an increase of the activation diameter Da from 17.1 nm to 17.7 nm. The value of Da deduced from the magnetic viscosity measurements is similar to the size of clusters of Nd-based bulk amorphous alloys, which may be responsible for the hard magnetic property exhibited at room temperature.