We have calculated the theoretical lattice parameters, Bulk modulus, volume, energy, lattice parameters and magnetic moments for RB₆ (R=La, Ce, Pr and Sm) of CaB₆ type crystal structure with space group Pm3m using full potential linearized augmented plane wave (FP-LAPW) method. The bulk modulus was found to be 9.56 % higher for LaB₆ and 2.4% lower for CeB₆ compared to the experimental results Gupta et al. [4] and Ogita et al [5]. Magnetic moments for LaB₆, CeB₆ were found in qualitative agreement with the earlier reported results. The results based on generalized gradient approximation (GGA) were found and compared with local spin density approximation (LSDA) results for CeB₆ and SmB₆ as well.