All those being held in connection with the murder are linked to a group known as the Boot Boys and were arrested in an Oslo flat filled with Nazi memorabilia.
Fifteen-year-old Benjamin Hermansen was stabbed to death near his Oslo home on 26 January. Six suspects linked to a neo-Nazi group have been arrested and charged with the murder.
Schools throughout Norway flew their flags at half-mast and held a minute's silence.
Hundreds of people packed into an Oslo church for a private service led by Norway's chief Lutheran Bishop, Gunnar Staalseth.
"A wonderful young boy has become a victim of racism. The protests and cries against injustice have a deeper note: the belief that evil will not have the last word," said Bishop Staalseth in the eulogy.
Shock
The attack on Hermansen shocked Norwegians and has galvanised the campaign against far right groups throughout Scandinavia.
Anti-racism rallies were planned on Tuesday in Copenhagen and Stockholm to coincide with Hermansen's funeral.
All those being held in connection with the murder are linked to a group known as the Boot Boys and were arrested in an Oslo flat filled with Nazi memorabilia.
Hermansen - the son of a Norwegian woman and a Ghanaian man - was an active campaigner against racism.
Thousands of Norwegians attended an anti-racism rally last month at the scene of his killing.
The Norwegian Government says it is planning to step up efforts to clamp down on racially-motivated crime, although it has played down suggestions of a ban on neo-Nazi groups.
Police believe there are probably about 150 active hardcore neo-Nazis in Norway's population of 4.4 million.