The purpose of this research study is to test the safety of the study drug, lenalidomide, at different dose levels in people diagnosed with acute myeloid leukemia (AML) who have finished standard induction therapy and have had a partial or complete response to induction therapy. The investigators want to find out what effects (for example, side effects) the study drug, lenalidomide, has on people and their leukemia. The investigators also want to see if additional treatment (maintenance therapy) with lenalidomide will keep the leukemia from relapsing (coming back).