We study submonolayer Ag deposited Ge(001) surfaces at 90 K by scanning tunneling microscopy (STM). Silver atoms and their small aggregates on the surface are found as bright dots on the surface at 78 K. The Ag aggregates form small clusters, and move with the change of the buckling phase in the adjacent Ge dimer row at 180 K as observed in successive STM images. These are transient processes to the formation of a surface alloy between Ag and Ge.