For Ce- and Yb-based metallic systems, the competition between Kondo and RKKY interactions results in a great variety of ground states. When these rare-earth ions are located on the geometrically frustrated lattices, the magnetic order may be tuned by the introduction of magnetic frustration. Although the lattices are geometrically frustrated for the short range, nearest neighbor spin-spin interaction, often the conduction electron degree of freedom in metals takes over the longer-ranged interactions. Due to this reason, the effect of geometrical frustration in metals is not obvious. In this talk, I will present the frustration effect on two-dimensional, triangular lattice, metallic antiferromagnets.