Abstract The longitudinal and transverse responses of 12C, in the region of the quasi-elastic peak, have been calculated within a continuum shell model. In addition to the one-body currents also the contribution of meson exchange currents has been taken into account. We have considered nuclear final states with both one and two particles in the continuum. The sensitivity of the results to the uncertainties related to nucleon electromagnetic form factors has been studied. A comparison with the Fermi gas model is made to test the finite size effects. A study of the effects on the meson exchange currents related to the use of the dynamical pion propagator and of the pionnucleon form factor is presented. The comparison with the experimental data is done after the inclusion of the final state interaction effects within a phenomenological model.