I recently had the serpantine belt and another drive belt replaced in my '04 g35 sedan and noticed the service engine light came on shortly after. Will a serpantine belt or other belt change do that or would it be something else?

 

Get the code read .. it may be something else that triggered the check engine light .. and you happened to replace the belts

 

^ that

 

Go to autozone and get the code read from free and figure out the issue. It could of been a problem that just so happened to pop up that day which was close to the day you work on your belts, but has nothing to do with it.