Why do some of my homebrewed beers foam over after opening?

So far, I have made two beers. With each of them, there has been a few select bottles that foam out the top like crazy after having opened them. I do let the beer sit for a couple weeks after bottling. Usually I pour the beer right into my own mug just after opening, but sometimes I do drink out of the bottle. So, it usually happens when I open a bottle and let it sit for a minute. It foams for a good 5 or so minutes making it a messy cleanup!

What could be going on here? Am I doing something wrong? Have you experienced this before?