In its English-language radio broadcast, the group praised the Wednesday shooting that killed 14 people and wounded 21 others.
"Two soldiers of the Khilafah (caliphate) executed an attack on the Inland Regional Centre in San Bernardino, California," the IS radio broadcast said in English.
IS refers to the swathe of territory it controls in Syria and Iraq as an Islamic caliphate.
The group's Arabic-language radio broadcast earlier in the day had referred to the attackers as "supporters of the Islamic State."