  We consider a general effective Lagrangian for couplings of a Higgs boson to
the top-quark to dimension-six operators including CP violation effects.
Constraints on some of them are derived from the $Z\to b\bar b$ data. We study
the process $e^+e^- \to t\bar t H$ to probe the non-standard couplings. We find
that at a linear collider with a c. m. energy $\sqrt s \sim 0.5-1.5$ TeV and a
high luminosity of 10-1000 fb$^{-1}$, these non-standard couplings may be
sensitively probed.
