  The antiferromagnetic correlation plays an important role in high-T$_{c}$
superconductors. Considering this effect, the magnetic excitations in n-type
cuprates near the optimal doping are studied within the spin density wave
description. The magnetic excitations are commensurate in the low energy regime
and further develop into spin wave-like dispersion at higher energy, well
consistent with the inelastic neutron scattering measurements. We clearly
demonstrate that the commensurability originates from the band splitting and
Fermi surface topology. The commensurability is a normal state property, and
has nothing to do with d-wave superconductivity. The distinct behaviors of
magnetic excitation between the n-type and p-type cuprates are further
discussed. Our results strongly suggest the essential role of antiferromagnetic
correlations in the cuprates.
