...but I would suppose that overthrowing the government would only be close to legal if the government does something wildly unconstitutional or so. Otherwise, this might apply:

Whoever knowingly or willfully advocates, abets, advises, or teaches the duty, necessity, desirability, or propriety of overthrowing or destroying the government of the United States or the government of any State, Territory, District or Possession thereof, or the government of any political subdivision therein, by force or violence, or by the assassination of any officer of any such government; [...] Shall be fined under this title or imprisoned not more than twenty years, or both, and shall be ineligible for employment by the United States or any department or agency thereof, for the five years next following his conviction.

Title 18, U.S.C., § 2385

Beck and Norris certainly didn't anything illegal as they was just "joking", but they certainly don't have the right to actually do anything they were talking about.