We report a study of structural, electronic and dynamic properties of Li3Bi and Li2NaBi via density functional theory. It is found that Li3Bi and Li2NaBi show semiconducting property with an indirect electronic band gap. The calculated structural and electronic parameters (lattice parameters, bulk modulus, bulk modulus derivation) are in a good agreement with the available experimental data. Full phonon spectra of Li3Bi and Li2NaBi materials in the Rock Salt structure were collected using the linear response method. At 0 GPa pressure, Li3Bi is dynamically stable while Li2NaBi, which can be synthesized from Li3Bi by replacing one Bi atom with the Na atom, is unstable. In this study we searched to find the pressure value that makes Li2NaBi dynamically stable. Calculations showed that the Li2NaBi structure becomes stable when 8.62 GPa pressure is applied to the Li2NaBi structure. This study is thought to give direction to the future studies.