owning a gun is in the american consitution. american constitution != the human rights.
http://www.hrweb.org/legal/udhr.html
this is a link to the human rights. the one you'll most likely refer to is article 17:
Article 17
1. Everyone has the right to own property alone as well as in association with others.
2. No one shall be arbitrarily deprived of his property.
now, if there is a law, set down by a government etc. which lives up to the human rights, banning guns, then you will not be arbitrarily deprived of the property which is your gun.