The answer depends on which state you live in. It also depends on whether you purposely provided your gun to the person who committed the crime or if, for example, it was stolen from you. If you provide your weapon to someone who commits a crime, the answer also turns on the kind of person who received the weapon –depending on your state, providing a weapon to a convicted felon, a non-criminal who goes on to commit a crime, or a minor all incur different penalties.
To learn more about the gun laws in your state see Gun Control Laws, and click the link to your state under the section entitled "Gun Laws by State".
Some states impose only relatively minor penalties on people who provide weapons to criminals. For example, in Kansas it is a class A nonperson misdemeanor to "knowingly sell, give, or otherwise transfer any firearm" to a convicted felon. Note that you must "knowingly" provide the firearm, which means that if you did not know (or there was no way you could reasonably have known) that the person was a convicted felon, you can probably avoid liability (although other laws may apply).
In contrast, other states like Hawaii pin the liability for any damage caused by a firearm on the weapon's owner, whether or not the owner provided the weapon to a felon or person without a criminal past. But even under this stricter state law, an owner can avoid liability if the owner was not in possession of the firearm at the time of the crime, the weapon was taken without the owner's permission, and the owner reported the theft (or had not discovered the theft, or was not reasonably able to report the theft) before the crime occurred.
Additionally, some states have made it a crime to provide a weapon to a minor (or, for parents, failing to prevent a minor from illegally carrying a weapon). For more on this topic, see Can parents be punished if their child possesses firearm? and What are the penalties for providing a firearm (or making one accessible) to a minor?
Penalties for violating firearms laws can include serious fines and long prison terms. If you have specific questions or are facing firearms-related charges, contact an experienced criminal defense attorney.