Inelastic incoherent neutron scattering techniques have been used to study the optic vibrations in hydrides of Nb and Ta for hydrogen concentrations between 44 and 49 at.% in the case of Nb and 42 at.% for Ta and at temperatures between 10 and 295 K. In all cases the first harmonic of the singlet fundamental vibration could be observed with an anharmonic shift of 3-5% to lower energies. In addition, evidence is presented for the first time of a combination band corresponding to the simultaneous excitation of the singlet and doublet fundamental vibration corresponding to out-of-plane and in-plane motion, respectively, of the proton on its tetrahedral site. These modes are coupled by anharmonic interactions which are described by a three-dimensional anharmonic-oscillator model of tetragonal symmetry (4̄2m) appropriate to hydrogen in bcc metals. This analysis using both the present data as well as previous work by other authors gives a consistent picture of anharmonicity in the bcc metal hydrides. In addition, splittings and/or broadening of the observed vibrational peaks for some concentrations or temperatures could be correlated with recent, new information on the high-concentration, low-temperature portion of the NbHx phase diagram.