rpm needle stuck and then drop rapidly when turn off
 

Not sure if this is an issue but I noticed my happened more and more lately. When I placed the car in park, my rpm is about 700. For most part, the rpm dropped smoothly down to 0. But there are times when I shut off the car, the rpm needle would jumped up tiny bit and stay there just a fraction of a second and then dropped down rapidly. Is this something to be concern or no?