2002 Explorer

My 2002 Explorer starting having the following issue: Once I start driving the door locks keep clicking and the beeping sound starts. This does not happen all the time. However this evening it started on the way home and once home every 15 to 20 min the alarm sounded. Had to keep turning off the alarm. My door light on the dash is staying on even after I check all the doors. This causes the the doors not to auto lock Any ideas would greatly b appreciated?