We performed ^75As-NMR measurements to investigate the normal-state magnetic properties of CeRh_2As_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_2As_2. With regard to spin fluctuations, the temperature dependence of the nuclear spin-lattice relaxation rate 1/T_1 arising from the 4f electrons decreases from high-temperature constant behavior on cooling at

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... 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_2As_2.