Government security adviser Niclas Kvarnström forgot a notebook at last week's Nato summit in Turkey, newspaper Dagens Nyheter (DN) has reported.
Government Offices have confirmed the information, but do not want to answer what the notebook contained. They have downplayed the security risk.
"Niclas Kvarnström has assessed that the notebook does not contain any classified information," press officer Matilda Nehlmark told DN.
Henrik Landerholm, one of Kvarnström's predecessors as national security adviser, resigned in January 2025 after it emerged that he had forgotten documents containing classified information at a conference centre.
Landerholm was acquitted in the district court of the charge of negligence with classified information. The case will be heard in the Court of Appeal in September.