The leader of the far-right Golden Dawn party, Nikolaos Michaloliakos, has been formally charged with belonging to a criminal organisation.
Four more Golden Dawn MPs, a party leader in an Athens suburb and 15 other people face the same charges.
They were arrested on Saturday amid anger over the murder on 18 September of anti-racist musician, Pavlos Fyssas.
A man held for the stabbing told police he was a Golden Dawn supporter, though the party strongly denies any link.
The MPs arrested on Saturday were party spokesman Ilias Kasidiaris, Ilias Panayiotaros, Nikos Michos and Ioannis Lagos. It is the first time since 1974 that a party leader and MPs have been arrested.
It was an extraordinary moment to see the five MPs being escorted in handcuffs by armed police in balaclavas, BBC Athens correspondent Mark Lowen reports.
They will now return to police headquarters and are likely to be refused bail before their trial, our correspondent says.
Mr Panayiotaros told reporters before giving himself up: "Shame on them, the people will lift Golden Dawn higher."
A number of other warrants are believed to have been issued. The arrests were made by the anti-terrorism unit.
Police said guns and ammunition had been found at Mr Michaloliakos's home and that he did not have a licence for the weapons.
Golden Dawn issued a rallying call via a text message, saying: "We call upon everyone to support our moral and just struggle against the corrupt system!"
Its call for members to gather outside the police headquarters in Athens was answered by some 200 supporters who chanted slogans and waved Greek flags.
Makis Voridis, a politician with the governing New Democracy Party, told the BBC's Newshour that the police had made the right decision on the arrests.
He said: "This is an alleged party. It is actually, as the justice system has said, a criminal organisation... members of a legal, political, parliamentary party, do not participate in homicides."