Its hard to tell with the information given, but you should probably have it looked at. It is perfectly normal for the oil pressure to drop significantly when you are stopped (at a light, etc.) but as soon as you hit the gas that needle should go right to the top (3 on my 420SEL) if, under normal driving circumstances it does not go all the way up you have lost pressure, either because your pump is not working to full capacity, your oil is moving sluggishly (due to a partial block or something in the oil) or a lack of pressure in the system (oil is getting out somewhere). The last thing you want is an engine that is not getting the oil it needs. Imagine what would happen to your hand if you cut off all blood supply to it for five minutes. Chances are you would never have use of it again. Same with your engine. It could be something pretty simple. Check your oil level. If it is down, find out why. If it is not, change it, and check out the breather hoses for sludge build up. Check the seal on the dipstick to make sure it is in good shape and sealing well to provide internal pressure. If none of that helps get professional help. No idea how much it might cost, but you can bet it'll be much much less than what it will cost later, if you do nothing now.