Top quark pair production and decay into 6 fermions at linear colliders

The production of a t\bar{t}-pair and its decay into a 6 fermion final state of different flavours in e+e- annihilation at centre of mass energies typical for linear colliders is analyzed in the framework of the Standard Model. The results of calculation based on exact matrix elements at the tree level and full 6 particle phase space are compared with a few different approximations. It is shown that the effects related to off-shellness of the t\bar{t}-pair and background contributions are sizable both in the continuum and at the threshold.