  We report on a lattice determination of the mass of the exotic $1^{-+}$
hybrid meson using an improved Kogut-Susskind action. Results from both
quenched and dynamical quark simulations are presented. We also compare with
earlier results using Wilson quarks at heavier quark masses. The results on
lattices with three flavors of dynamical quarks show effects of sea quarks on
the hybrid propagators which probably result from coupling to two meson states.
We extrapolate the quenched results to the physical light quark mass to allow
comparison with experimental candidates for the $1^{-+}$ hybrid meson. The
lattice result remains somewhat heavier than the experimental result, although
it may be consistent with the $\pi_1(1600)$.
