Yes, fidgeting is a sign of nervousness. When you are nervous, like when you are in a crowd of people you don't know, or if you are about to give a speech, you may resort to safety behaviors which serve to help you through the anxiety of the situation or event. So when you nervous, and you are in a crowd of strangers, you may resort to fidgeting, or fiddling with your personal effects in your pockets, as it helps to distract yourself from the nervousness you feel. But when you resort to safety behaviors such as fidgeting, it decreases your concentration and focus, and hence will affect your performance in negative ways, such as not being able to respond to strangers who talk to you, or not being able to deliver your speech when called upon.
To help you reduce your safety behaviors such as fidgeting, you need to understand how performance anxiety develops, and what you can do to address it, and hence stop your fidgeting when nervous. The following video explains all this: