Change oil light on

I have a 2004 Buick Century custom. Did an oil
change last November. About a week ago I noticed
that the "Change oil soon" light does not turn off
after starting the car, like the seat belt light and the
other lights that come on when you start the car
do. It eventually goes off after 10 or 15 minutes of
driving. Just wondered if it's something I need to
worry about and what I should do about it.