Robertson, also known as Abu Taubah, was accused of teaching another man how to participate in violent jihad missions overseas.
On Friday, U.S. Judge Gregory Presnell sentenced Robertson to a total of 20 months for both convictions.
But Robertson has spent the last three and a half years in prison, according to his attorney Daniel Broderson, which is more time than his actual sentence.
He was convicted on the weapons charge in 2012 and tax fraud in 2014, the judge said.
As a condition of his release, Robertson was put on probation for three years.
“As the judge remarked, he should not have spent that much time in jail based on the crimes he committed,” Broderson said after the sentencing. “He’s going to go on with his life to the best of his ability.”
Robertson had faced increased sentencing of up to 20 years for allegedly promoting terrorism through these crimes.
According to federal prosecutors, Robertson falsified tax documents to fund recruiting efforts for an al-Qaida base overseas.
This allegation was based on seized books, court-authorized surveillance and the man who says Robertson trained him, Jonathan Jimenez.
Jimenez plead guilty in 2012 of lying to FBI agents and falsifying income-tax documents, records show. He is serving a 10-year prison sentence.
Presnell determined there wasn’t enough evidence to prove the terrorism claim.
At Friday’s sentencing, Presnell said he had received hundreds of emails from people asking him to hand down a maximum sentence.
He read one of the emails, which said, “Islam must be stopped and redirected back to the Middle East.”
In his comments to the court, Presnell said the U.S. is probably the most religiously tolerant country in the world.
The Council on American-Islamic Relations in Florida supported the judge’s decision. The organization’s chief executive director, Hassan Shibly, spoke after the sentencing on behalf of Robertson and his family.
“The judge sent a strong message to the government that it cannot lock people up for preaching and teaching Islam by falsely misrepresenting possessing Islamic literature and teaching Islam as equating to sympathizing with terrorism,” Shibly said.