Mass graves in Slovenia were created in Slovenia as the result of extrajudicial killings during and after the Second World War. These clandestine mass graves are also known as "concealed mass graves" or "silenced mass graves" because their existence was concealed under the communist regime from 1945 to 1990.

Onek is a settlement in the hills east of Kočevje in southern Slovenia. The area is part of the traditional region of Lower Carniola and is now included in the Southeast Slovenia Statistical Region.