The potential energy surface for methyl cation is calculated using an extrapolated full coupled-cluster/complete basis set (FCC/CBS) theory. The equilibrium C-H bond length is obtained as 1.0884 Angstrom. The vibrational energy levels of both CH3+ and CD3+ cations are computed using a variational method, based on the accurate potential energy surface. The fundamental frequencies in cm-1 are predicted to be 2942.27 (v(1)), 1377.82 (v(2)), 3108.29 (v(3)), and 1387.01 (v(4)) for CH3+, and 2082.99 (v(1)), 1070.31 (v(2)), 2339.99 (v(3)), and 1015.70 (v(4)) for CD3+, respectively.