The federal judge said that he had granted a 30-day stay of the ruling at the request of California Attorney General Rob Bonta, a move that would allow Bonta to appeal it.
"Today's decision is fundamentally flawed, and we will be appealing it," Bonta said in a statement.
Seven states, including California, and the District of Columbia have enacted laws banning assault weapons, according to the Giffords Law Center, a gun-control group.
Gun control is a politically divisive subject in the United States, which has experienced a significant number of deadly mass shootings at schools and other public venues for decades.
California Governor Gavin Newsom described Friday's overturning of the ban on assault weapons as a direct threat to public safety and called it a "disgusting slap" in the face to those who have lost loved ones to gun violence.
"The fact that this judge compared the AR-15 – a weapon of war that's used on the battlefield – to a Swiss army knife completely undermines the credibility of this decision," the governor said in a statement.
"Like the Swiss army knife, the popular AR-15 rifle is a perfect combination of home defense weapon and homeland defense equipment," the judge had said in the order filed on Friday.