  Two-dimensional van der Waals compounds with magnetic ions on a honeycomb
lattice are hosts to a variety of exotic behavior. The magnetic interactions in
one such compound, MnPSe$_3$, are investigated with elastic and inelastic
neutron scattering. Magnetic excitations are observed in the magnetically
ordered regime and persist to temperatures well above the ordering temperature,
$\rm T_N$ = 74 K, consistent with low dimensional magnetic interactions. The
inelastic neutron scattering results allow a model spin Hamiltonian to be
presented that includes dominant intralayer interactions of $J_{1ab}$=0.45 meV,
$J_{2ab}$=0.03 meV, $J_{3ab}$=0.19 meV, and appreciable interlayer interactions
of $J_c$=0.031(5) meV. No evidence for anisotropy in the form of a spin-gap is
observed in the data collected. The measurements on MnPSe$_3$ are contrasted
with those on MnPS$_3$ and reveal a large increase in the interlayer exchange
interactions in MnPSe$_3$, despite the quasi-2D magnetic behavior.
