In the theoretical framework of the Left-Right Symmetric Model, the lightness of the left-handed neutrinos can be explained by the See-Saw mechanism, if neutrinos are Majorana particles and if right-handed heavy neutrinos exist. The search for new heavy right-handed Majorana neutrinos N can first be performed at CERN Large Hadron Collider. In pp collisions, N is produced together with the associated charged lepton in the decay of a right-handed charged boson Wr. These new particles can be discovered after 3 years of LHC running at high luminosity if m(Wr) and m(N) are respectively smaller than 6 and 4 TeV. In the post LHC era, very accurate measurements can be performed with an e+e- linear collider such as CLIC, where a large amount of e+e- -> Z' -> NN events are likely to occur. The masses of the new Z' neutral boson and of N can indeed be measured with an accuracy of respectively 0.01% and 0.19%.