http://www.ncsl.org/research/civil-and-criminal-justice/possession-of-a-firearm-by-the-mentally-ill.aspx

Almost every State has a specific law intended to control the possession of firearms by those who are Mentally Ill. Unfortunately, most of these laws are rather vague and hard to enforce.

There is a Federal Law regulating this issue as well:

Under 18 U.S.C. § 922(d), it is unlawful for any person to sell or otherwise dispose of any firearm or ammunition to any person knowing or having reasonable cause to believe that such person “has been adjudicated as a mental defective or has been committed to any mental institution.”

Are you familiar with what your State has to say on the topic?