  We study a topological band degeneracy in non-Hermitian systems with
parity-time ($PT$) and parity-particle-hole ($CP$) symmetries. In
$d$-dimensional non-Hermitian systems, it is shown that $(d-1)$-dimensional
exceptional surfaces can appear from band touching thanks to $PT$ or $CP$
symmetry. We investigate the topological stability and zero-gap quasiparticles
for the exceptional surfaces due to the band degeneracy. We also demonstrate
the band degeneracy by using lattice models of a topological semimetal and a
superconductor.
