The former president was being investigated by police in relation to a failed military attempt to topple the West African country's government in November.
Gunmen attacked military barracks, a prison and other locations in Sierra Leone on November 26.
They freed about 2,200 inmates and killed more than 20 people.
Authorities later said that it was a foiled coup led mostly by Koroma's bodyguards.
Koroma, who condemned the attacks in a statement shortly after they happened, was summoned for questioning in December as part of the police investigation.
On Wednesday (January 3), the charges were read out to the former president as he stood in the dock and some of his supporters cried in the courtroom.
Another 12 people have been charged with treason, including Koroma's security detail.
That's according to the government on Tuesday (January 2).
The accused, which included ex-police and correctional officers, were arraigned before a magistrate in the capital Freetown on Tuesday (January 2), the information ministry said in a statement.
