  We performed $^{75}$As-NMR measurements to investigate the normal-state
magnetic properties of CeRh$_2$As$_2$, a recently-discovered heavy-fermion
superconductor. The magnitude and temperature dependence of the Knight shift at
the As(2) site indicate easy-plane-type magnetic anisotropy in CeRh$_2$As$_2$.
With regard to spin fluctuations, the temperature dependence of the nuclear
spin-lattice relaxation rate $1/T_1$ arising from the 4$f$ electrons decreases
from high-temperature constant behavior on cooling at $\sim$ 40~K, which is
typical behavior of heavy-fermion systems. In addition, $1/T_1$ becomes
constant at low temperatures, suggesting spatially two-dimensional
antiferromagnetic fluctuations. Two-dimensional magnetic correlations in the
real space are quite rare among heavy-fermion superconductors, and they may be
a key factor in the unique superconducting multi-phase in CeRh$_2$As$_2$.
