'Service Engine Soon" light problem in Dashboard
 

Hello everyone,
I have a 2000 Oldsmobile Intrigue GX with a mileage of about 84775 miles.I bought it at the end of May this year and it was running quite OK since then.But yesterday as I went to one of my friend's place and kept the engine idling for about 3-4 minutes,the "Service Engine Soon" light pops up in the Dashboard.Can anyone tell me whether this is a serious issue which needs to be resolved immediately or not and in case if i need to fix it up,how much it might cost?In addition,what could be the probable reason for this kind of problems?

Thanks in advance.