Using first-principles density functional theory, the zone-center phonon spectrum, mode oscillator strengths and Raman tensor coefficients are computed for the relaxor ferroelectric Na1/2Bi1/2TiO3 (NBT) in R3c phase. Subsequently, these quantities are used to compute the Infrared (IR) reflectivity and Raman intensity spectrum. The E symmetry modes at 246, 296, 580 cm-1 and A1 symmetry modes at 256, 266, 568 cm-1are found to have high oscillator strengths. The computed Raman coefficients are also found to be significant for aforementioned A1 modes. The computed IR reflectivity and Raman spectra are expected to provide benchmark first-principles theroertical results for the symmetry assignment of experimental spectra of NBTin R3c phase. ©2016 IOP Publishing Ltd.