yes it sounds normal,my srs light is the last light to go off,all cars do this,its the last light to go out,it stays on for just a few seconds longer than all the other light,mercedes are not the only cars that do this all cars do,but if the light is coming on while driving down the road,and stays on or flashes something else may be wrong.you may want to have it diagnosed,could be a loose connector end on the air bag.as long as the light is on the air bag wont deploy,but once the light shuts off your fine.