Beginning from Maxwell's equations and by considering the second-order nonlinear polarization related to the optical activity as the perturbation of linear polarization, we investigate the propagation behavior of the paraxial Gaussian light which acts as incident light in the optically active medium Bi12SiO20 and utilize the Minkowski and Abraham momenta to obtain the expressions of optical momentum and angular momentum in Bi12SiO20 crystals. Further, we obtain that the ratio of Minkowski momentum to Abraham momentum is not equal to the square of the refractive index of the crystal because of the existence of optical activity. In the Minkowski picture, because of the coupling of the angular momentum between the light and the crystal, the angular momentum of the light field is not conserved, whereas the total angular momentum of the light and crystal is conserved.