The structural and electronic properties of NACL in Rocksalt and CsCl phases are investigated under high pressure using total energy minimization techniques. The Kohn-Sham equations are solved within the local density approximation using the pseudopotential method with a plane wave basis set. The calculated structural properties such as lattice parameter, bulk modulus and its pressure derivative are in reasonable agreement with the experiment. At zero pressure the Rocksalt phase is found to be lower in energy than a hypothetical CsCl structure. However, we predict a phase transition into CsCl structure at high pressures. The electronic band structure at normal and high pressures is also calculated. It is found that metallization occurs for Rocksalt and CsCl structures at ultrahigh pressures.