The group which calls itself "Breaking the Wall of Silence" said their government should also investigate past human rights violations, SABC radio news reported.
This includes the disappearance of Swapo guerrillas and exiles.
Tutu said it would be improper for him to interfere in the domestic affairs of another country.
The group's request follows the publication of German pastor Siegfried Groth's book, Namibia the Wall of Silence. It deals with Swapo's abuse of detainees during the liberation struggle.