I think I've seen this reported before, and usually it means you need to give the windshield a good thorough cleaning. Sometimes some wax or tree sap or other contaminant gets on the windshield, and if the wipers aren't cleaning the windshield off well, the sensor thinks it needs to keep them going more than necessary. It might also be time to change your wiper blades if they are old, or a windshield cleaning doesn't do the trick.
2011 Jerez Black/Fox Red E90 M3 DCT, ZCP, ZCV, ZCW, ZP2, BMW Apps
2004 VW R32 (track car)