  We analyze explicit CP violation in the Higgs sector of the next-to-minimal
supersymmetric standard model which contains an additional gauge singlet field
N. It is shown that there is no mixing among scalar and pseudoscalar Higgs
fields in the two Higgs doublets, and scalar-pseudoscalar mixings could exist
between two Higgs doublets and the singlet N, and between N itself. CP symmetry
is conserved in the extreme limits of < N > >> v, < N > << v, and tan beta >>
1. In the region of < N > = O(v) and tan beta = O(1), large scalar-pseudoscalar
mixings are realized, and this effect can reduce the lightest Higgs mass. The
mass difference between no mixing and mixing case is about 10 - 30 GeV. The
neutron electric dipole moment in this model is consistent with the present
experimental upper limit provided that squark and gaugino masses are heavy
enough of O(1) TeV.
