Is it a problem? Does the performance suffer?
Newer cards have a feature that lowers the clock significantly when it is not under heavy stress to save power. Sure, you could lock it to the max clock, but that would be a waste of power and money. Only do that if it is lowering the clock and causing performance problems, like during games, but if it's some type of light 3d software app, and it's not suffering performance-wise, don't worry about it.