  We use neutron scattering to study the Pr$^{3+}$ crystalline electric field
(CEF) excitations in the filled skutterudite PrOs$_4$As$_{12}$. By comparing
the observed levels and their strengths under neutron excitation with the
theoretical spectrum and neutron excitation intensities, we identify the
Pr$^{3+}$ CEF levels, and show that the ground state is a magnetic
$\Gamma_4^{(2)}$ triplet, and the excited states $\Gamma_1$, $\Gamma_4^{(1)}$
and $\Gamma_{23}$ are at 0.4, 13 and 23 meV, respectively. A comparison of the
observed CEF levels in PrOs$_4$As$_{12}$ with the heavy fermion superconductor
PrOs$_4$Sb$_{12}$ reveals the microscopic origin of the differences in the
ground states of these two filled skutterudites.
