Many mobile manipulation tasks require the robot to be accurately localized with respect to the object where the manipulation has to be executed. These tasks include autonomous docking and positioning as well as pick and place or logistics tasks. State-of-the-art approaches to the problem commonly assume that the environment is static and localize the robot with respect to predetermined locations. In this paper, we present an approach that relaxes the static assumption and enables a robot to accurately localize with respect to a reference object that could be moved in the environment. The core of the paper is an extension of the generalized ICP method to handle multiple rigid bodies that move independently to each others. Experiments in both simulated and real world scenarios show that our approach is able to localize the robot with respect to a moved object with an accuracy of less than one centimeter.