The harmonic frequencies omega (est) of (C6H6)-C-12 calculated by combining the anharmonic constants from a DFT quartic force field with the experimental fundamentals, are compared with harmonic frequencies, omega (calc) obtained with different theoretical methods. One set of omega (calc) was derived by Martin, Taylor and Lee by ab initio CCSD(T) theory, the others have been calculated by us by means of the density funcional theory DFT with B3LYP, B3PW91, B3P86 and mPW1PW hybrid functionals. The mean absolute deviation between ab initio omega (calc) and omega (est) is 6.8 cm(-1) while between DFT omega (calc) and omega (est) is between 8.6 and 10.5 cm(-1). Moreover the DFT omega (calc) show a small systematic underestimation of the CH stretching vibrations.