  For a reliable prediction of the NMSSM Higgs boson signatures at present and
future high-energy colliders and a proper distinction of the NMSSM and MSSM
Higgs sector the precise knowledge of the Higgs boson masses including
higher-order corrections is indispensable. In this paper, the one-loop
corrections to the neutral NMSSM Higgs boson masses and mixings are calculated
in three different renormalisation schemes. In addition to the $\bar{DR}$
renormalisation scheme, existing in the literature, two other schemes are
adopted. Furthermore, the dependence on the value of the top quark mass is
investigated. The resulting Higgs mass corrections have been compared and the
residual theory error due to missing higher-order corrections can be estimated
to be of the order of 10%.
