  We study the muon anomalous magnetic moment a_\mu = (g_\mu - 2)/2 in a
supersymmetric U(1)' model. The neutralino sector has extra components from the
superpartners of the U(1)' gauge boson and the extra Higgs singlets that break
the U(1)' symmetry. The theoretical maximum bound on the lightest neutralino
mass is much smaller than that of the Minimal Supersymmetric Standard Model
(MSSM) because of the mixing pattern of the extra components. In a U(1)' model
where the U(1)' symmetry is broken by a secluded sector (the S-model), tan\beta
is required to be < 3 to have realistic electroweak symmetry breaking. These
facts suggest that the a_\mu prediction may be meaningfully different from that
of the MSSM. We evaluate and compare the muon anomalous magnetic moment in this
model and the MSSM and discuss the constraints on tan\beta and relevant soft
breaking terms. There are regions of the parameter space that can explain the
experimental deviation of a_\mu from the Standard Model calculation and yield
an acceptable cold dark matter relic density without conflict with collider
experimental constraints.
