  We study the axial U(1)A symmetry of Nf = 2 QCD at finite temperature using
the Dirac eigenvalue spectrum. The gauge configurations are generated employing
the Mobius domain-wall fermion action on 16^3x8 and 32^3x8 lattices. The
physical spatial size of these lattices is around 2 fm and 4 fm, respectively,
and the simulated temperature is around 200 MeV, which is slightly above the
critical temperature of the chiral phase transition. Although the Mobius
domain-wall Dirac operator is expected to have a good chiral symmetry and our
data actually show small values of the residual mass, we observe significant
violation of the Ginsparg-Wilson relation for the low- lying eigenmodes of the
Mobius domain-wall Dirac operator. Using the reweighting technique, we compute
the overlap-Dirac operator spectrum on the same set of configurations and find
a significant difference of the spectrum between the two Dirac operators for
the low-lying eigenvalues. The overlap-Dirac spectrum shows a gap from zero,
which is insensitive to the spacial volume.
