Carbon fiber reinforced plastic (CFRP) exhibits high specific elasticity and a low coefficient of thermal expansion. Therefore, CFRP is considered to be a suitable material for fabricating reflectors for high-precision, space-based astronomical observation systems. However, non-negligible out-of-plane thermal deformation on CFRP reflectors may occur due to errors in the fiber orientation of each layer. In addition, out-of-plane thermal deformation can be generated because of non-uniform temperature conditions even when no fiber orientation error exists. In this study, the out-of-plane thermal deformation of a CFRP reflector model due to normally distributed fiber orientation errors was probabilistically examined, and methods to mitigate the effect of fiber orientation errors were investigated. The Monte Carlo method was used for analysis. The results demonstrated that increasing the number of layers using thin prepregs was found to be an effective method to mitigate not only the effect of fiber orientation errors, but also out-of-plane thermal deformation modes caused by non-uniform temperature distributions. Furthermore, it was found that the stacking sequence should be appropriately determined to reduce the effect of fiber orientation errors.