The Oddest Feeling

So lately I've been having these random localized spasms or quivering of muscles in various places like in my hamstrings, triceps, forearms. It doesn't happen too frequently but I come to worry that my body is doing something abnormal. I feel as if though I am not stretching enough and that ultimately my body will be susceptible to contractures and such. I know the importance of exercise and to be honest, I do feel as if though my joints are stiff, not incredibly stiff with discomfort. Again, this quivering of my muscles is awkward. Anyone ever have this happen to them? What do you think it could be? Any information or advice would be greatly appreciated. Thanks.