  Although the studies of tensor structure of the Higgs boson interactions with
vector bosons and fermions at CMS and ATLAS experiments have established that
the $J^{\mathrm{PC}}$ quantum numbers of the Higgs boson should be $0^{++}$,
small CP violation in the Higgs sector (up to 10% contribution of the CP-odd
state) cannot be excluded with the current experimental precision. We review
possibilities to measure CP violating mixing angle $\Psi_{\mathrm{CP}}$ between
scalar and pseudoscalar states, at a linear electron-positron collider, at
center-of-mass energy of 1 TeV.
