Vano Merabishvili, the interior minister, said that all those detained on Wednesday were supporters of the fugitive opposition leader, Igor Giorgadze.
Giorgadze is wanted on charges of attempting the assassination of Eduard Shevarnadze, the then president, in 1995.
Those seized in pre-dawn raids nationwide involving 450 police officers are reported to include the leader of the Conservative Monarchist Party, Temur Zhorzholiani, two regional representatives of the Justice party and the leader of the Anti-Soros Movement.
"They will be charged under article 315 of the Georgian criminal code - plotting against the state and overthrowing the government," Merabishvili said, without giving details of the alleged plot.
Earlier, state-owned and private television channels showed security forces in black masks and armed with Kalashnikovs leading several of the opposition figures into waiting cars.
Georgian television stations showed piles of dollar bills allegedly confiscated during the searches.
Mikhail Machavariani, the deputy speaker of the Georgian parliament, said the money had been smuggled in from Russia.
Last week, the president himself, Mikhail Saakashvili, accused Russia of conspiring to replace him with Giorgadze.
Giorgadze lives in hiding but held a high-profile press conference in May in Moscow and has been offered political asylum by Russia, prompting an angry reaction from the pro-US government in Tbilisi.
Saakashvili's popularity has
Interviewed by Russia's state-run Channel One television on Wednesday, Giorgadze said the arrests were part of a campaign of repression ahead of municipal elections in October. "This is the begining of the end of Saakashvili," he predicted.
In a separate interview with Russia's Echo Moscow radio, he also warned that "if the authorities raise their stick ... then we will answer with a stick."
Relatives of Giorgadze said they had been searched by police and that searches had also been conducted in the office of Giorgadze's charity.
Saakashvili's popularity has plunged halfway through his five-year term.
In March, the Organization for Security and Cooperation in Europe's envoy to Georgia expressed concern about media freedoms, due process and independence of the judiciary.