Dishwasher

I am getting back flow of water into the base of my dishwasher. Once the the dishwasher finishes washing the dishes, over a short period, water begins to collect in the bottom of the dishwater; it gets to a certain level and stays there until the dishes are washed again. Initially the bottom of the dishwasher is dry; Please tell me what is the problem? And what I need to do to repair it?

Thanks,
wea1234567@gmail.com

Here is a good install sheet
http://products.geappliances.com/MarketingObjectRetrieval/Dispatcher?RequestType=PDF&Name=31-30515.pdf
Check the drain line installation, see Page 6, for either the air gap or the loop height.