Answer
Yes, Håvard Nordtveit has scored an own goal before. It occurred during a Bundesliga match between his team 1. FSV Mainz 05 and FC Bayern Munich on 19 October 2013. Nordtveit attempted to clear a cross from Bayern's Franck Ribéry, but inadvertently directed the ball into his own net. The own goal contributed to Mainz's 4–1 defeat in that match.