We have recently demonstrated the potential of a new class of thermoelectric materials mainly composed of chalcogen and pnictogen atoms, namely BiCuSeO. Although its crystallographic structure is very simple, it presents a very low lattice thermal conductivity at room temperature which is two times lower than in well known thermoelectric families of skutterudites and clathrates. Moreover, our calculations show that the lowest optical mode is at about 7 meV, an energy similar to filled skutterudites and higher than in most clathrates. It was then proposed that an increase of the anharmonicity due to the electron lone pair of the pnictogen atoms could be the reason behind this low thermal conductivity. In this proposal, our interest is to study the phonon properties of the BiCuSeO material and possible anharmonic effects in a wide temperature range by neutron INS in order to elucidate the mechanism responsible for the low values of thermal conductivity in BiCuSeO.