No problem. I have the same situation as yours since ..

H-1B is a visa for temporary alien workers to stay in USA to perform their duties for their sponsors. Your H-1B can be extended for three more years IF your I-140 have been approved prior to the end of the H-1B six years duration. After you filed your H-1B extension,as per "AC21", the alien is allowed to work for up to 240 days prior to receipt of the Approval Notice as long as the H-1B extension was filed timely.