  We report on lattice calculations of the $B$ meson decay constant and the
B-parameters using the NRQCD action for heavy quark. We performed a set of
calculations at three lattice spacings in the quenched approximation in order
to investigate the systematic uncertainty associated with the lattice
discretization. Our results indicate that the systematic error is under good
control for f_B and B_B. We also present preliminary results from our
unquenched simulation.
