German reports say the group of far-right and ex-military figures planned to storm the parliament building, the Reichstag, and seize power, BBC reported.
A German man referred to as a prince called Heinrich XIII, 71, is alleged to have been central to their plans.
According to federal prosecutors, he is one of two alleged ringleaders among those arrested across 11 German states.
The plotters are said to include members of the extremist Reichsbürger [Citizens of the Reich] movement, which has long been in the sights of German police over violent attacks and racist conspiracy theories. They also refuse to recognize the modern German state.
An estimated 50 men and women are alleged to have been part of the group who are said to have plotted to overthrow the republic and replace it with a new state modelled on the Germany of 1871 - an empire called the Second Reich.
"We don't yet have a name for this group," said a spokeswoman for the federal prosecutor's office.
Raids took place in much of the country and two people were arrested in Austria and Italy, Germany's DPA news agency reported. Those detained were due to be questioned later in the day.
Justice Minister Marco Buschmann tweeted that a major anti-terror operation was taking place and a suspected "armed attack on constitutional bodies was planned".
The federal prosecutor said the group had been plotting a violent coup since November 2021.
Former members of the military were also a significant part of the coup plot, reports said. They included ex-elite soldiers from special units.
The plotters had already established plans to rule Germany, the federal prosecutor's office said. Members understood they could only realize their goals by "military means and violence against state representatives" and that included carrying out killings.
Public broadcaster ZDF reported that a former far-right member of the lower house of parliament, the Bundestag, was also part of the plot and was lined up to be installed as the group's justice minister, with Prince Heinrich as a leader.
SKH/PR