Prime Minister Najib Razak pledged last year to repeal the Sedition Act, widely seen as oppressive. Critics slammed the fresh arrests under the law, believed to be in connection with calls to protest against alleged fraud during the May 5 election.
Najib's Barisan Nasional (National Front) coalition won the election, extending its 56-year rule, but the opposition has alleged that fraud marred the polls and cost them victory.
Adam Adli Halim was charged under the Sedition Act over a statement made at a public post-election forum on May 13, and had been held in custody for five days until Thursday, said his lawyer Fadiah Nadwa Fikri.
After being charged, he was released on bail.
The 24-year-old is accused of calling on people to protest at the election results, Fadiah said. He pleaded not guilty to the charge, which carries a penalty of up to three years in jail.
Also Thursday senior opposition politician Tian Chua and activist Haris Ibrahim were detained under the Sedition Act. Another opposition politician was also detained, lawyer Malik Imtiaz said.
Malik did not immediately have further details. Kuala Lumpur police chief Mohmad Salleh declined to comment, saying he would make a statement later.
Police have previously said they are investigating those who challenge the government over the fraud claims.
Fadiah, the student's lawyer, slammed the use of the Sedition Act, which Najib pledged to repeal last year as part of a much-touted drive to strengthen civil liberties, after criticism of its use mounted.
"It's clearly still being used to stifle dissent," Fadiah told AFP. "The law is open to abuse... it's an infringement to freedom of speech and freedom of assembly."
London-based human rights group Amnesty International has slammed Malaysia's use of the Sedition Act.
"The Malaysian authorities must ensure that peaceful political dissent is protected both in law and practice," it said in a statement on Wednesday.
Malaysian activists and the opposition have dismissed Najib's moves to amend a series of security laws to guarantee greater civil liberties as window-dressing to appease voters.
Police said earlier this month they may pursue sedition charges against speakers at a May 8 mass stadium rally organised by opposition leader Anwar Ibrahim to launch nationwide protests against alleged poll fraud.
The opposition claims the voter rolls used in the national polls were full of irregularities, such as huge numbers of voters registered in closely fought constituencies, allegedly to sway the results in favour of Barisan.
The government has denied the elections were unfair.
Barisan won 133 of 222 parliamentary seats, seven seats fewer than in the previous polls in 2008 but holding on to a comfortable majority. But they only gained 46.6 percent of the popular vote.