2005 focus just stopped running
 

I have an 05 focus and the other day I pulled up to a stop light and when the car stopped moving it just shut right off. Almost like I had turned the ignition key to off. I turned the key and it started right up and ran fine. Then a few days later did it again. It has done this about five times since. Any ideas on what this may be. Thanks

bad connection on the battery terminals try tightening the bolts