An eccentric bearing for an electrohydraulic piston pump assembly of a vehicle brake system includes a shaft configured to be driven in rotation about its axis, a bearing ring which is eccentric relative to the shaft, and rolling bodies between the bearing ring and the shaft. The rolling bodies have different diameters corresponding to a varying width of a gap between the bearing ring and the shaft. When the shaft is driven in rotation, an eccentricity of the bearing ring revolves around the shaft at half of the rotational speed of the shaft and drives pump pistons to perform a reciprocating movement. A rolling body cage is open between the two largest rolling bodies. The rolling body cage loads the rolling bodies into the tapering gap and ensures that the rolling bodies revolve on the shaft when the shaft is driven.