Don't worry. That step is VERY common. Most people these days are approved pending clearance (name check).
HERE is a link to a thread here on VJ all about people who are going through the same as you. Some peoples name check comes through fast (ours did) and others can take months. It really just depends. Our online status didn't change. The next thing it changed to was saying "your card is being made" or something like that after the name check cleared. Here is what our timeline looked like:
04.27.06 ~ AOS INTERVIEW @ 9:30am!!! (4 months 9 days after filing)
04.27.06 ~ AOS APPROVED!!! (pending FBI clearance) (4 months 9 days after filing)
05.16.06 ~ Welcome letter received!!! (4 months 28 days after filing)
05.22.06 ~ GREEN CARD IN THE MAIL!!! (5 months 3 days after filing)
check around with other people that went through the same local office you did to get an estimate of time it takes...but I wouldn't stress at all

Congrats on being approved