  We study the pair production of new heavy leptons within a new $U(1)'$
symmetry extension of the Standard Model. Because of the new symmetry, the
production and decay modes of the new heavy leptons would be different from
those of three families of the standard model. The pair production cross
sections depending on the mixing parameter and the mass of heavy leptons have
been calculated for the center of mass energies of $0.5$ TeV, $1$ TeV and $3$
TeV. The accessible ranges of the parameters have been obtained for different
luminosity projections at linear colliders. We find the sensitivity to the
range of mixing parameter $-1<x<1$ for the mass range $M_{l'}<800$ GeV at
$\sqrt{s}=3$ TeV and $L_{int}=100$ fb$^{-1}$
