The Jewish Defence League's Earl Krugel is also accused of attempting to blow up the office of an Arab-American congressman.
US District Judge Ronald Lew on Monday invalidated a plea bargain struck earlier between prosecutors and Jewish Defence League (JDL) for breaching the terms of the plea deal.
Under the deal, the 61-year-old Krugel pleaded guilty to conspiracy to violate the civil rights of worshipers at the King Fahd Mosque in Los Angeles and to a weapons charge linked to explosives that prosecutors said were intended to blow up the office of Representative Darrell Issa.
In return, he was to escape trial on more serious charges that include attempted arson, possession of a destructive device to further a crime of violence and soliciting someone to commit a crime of violence.
But instead of facing between 10 and 20 years behind bars under the plea agreement, Krugel could now face a minimum of 55 years in prison.
Lawyers in the case are barred from saying how Krugel allegedly breached his plea bargain deal, but his defence lawyer Peter Morris said he had cooperated with prosecutors and that the voiding of the deal was unjust.
Krugel was arrested along with fellow JDL leader and founder Irv Rubin, who died in November 2002 after authorities said he slashed his own throat and then threw himself off a prison walkway while awaiting trial.
Prosecutors alleged that Rubin and Krugel had wanted to send a "wake-up call" to Arabs and to show that the militant JDL was "alive in a militant way" by blowing up the mosque and the offices of Issa, who is of Christian Lebanese descent.
The alleged plot was thwarted when an informant alerted investigators and the two men were arrested at their homes and weapons and bomb-making equipment were seized from them.