Carl Dial, 23, of Palm Desert, pleaded guilty to felony arson with a hate crime enhancement last Thursday, according to court records.
He set fire to the Islamic Society of Coachella Valley on Dec. 11, more than a week after Syed Farook and his wife, Tashfeen Malik, opened fire on a group of county workers in San Bernardino on Dec. 2, killing 14 people.
Farook and Malik were later killed in a shootout with police. They had long been radicalized and were investigators believe the shootings were inspired by acts of international terrorism, authorities said.
No one was hurt in the mosque fire. Under the plea agreement, Dial will be sentenced to six years in prison on Feb. 29.
Police have not said how the fire was set or what motivated the arson. Witnesses said a Molotov cocktail-style firebomb was thrown into the building, NBC affiliate KMIR reported at the time. The Riverside County District Attorney's office declined to comment, citing the pending sentencing.
The fire caused significant damage, mosque member Saleh Saleh said Wednesday.
"You know, we forgive him," Saleh said in a phone interview. "I hope he will learn, we are equal," Saleh said.
Dial has been held in lieu of $150,000 bail since his arrest late Dec. 11.
NBC