There could be. Prom is perfect on paper, but in actuality, it's very different. Prom is always seen as the night you will get drunk/high and have sex (possibly for the first time), which is ungodly. The dancing, which isn't so much dancing anymore than it is just grinding (except for slow stuff), would be considered ungodly. It never fails that someone gets the bright idea to either try to or actually does spike the provided beverages - ungodly. While it can be a wholesome, God-friendly environment and night, society has gotten and will continue to get in front of that, to force people to bow to their standards. It's sort of mixed ground, but it's all about you, your school, and your city. Realistically, there will be drugs/alcohol consumed even if you don't hear about it.
Overall, is prom sinful or ungodly? No. The things people do at prom? Yes.
If you're wondering whether you'll offend God by going, you won't. Just don't get involved with the wrong things or people and you'll be fine.
1 Corinthians 15:33 (NIV)
"Do not be misled: 'Bad company corrupts good character.