The members of Hindu Rights Action Force (Hindraf) have been detained since December 2007 after they were held for organising unprecedented anti-government protests against alleged marginalisation of ethnic Indians in Malaysia.
More than 20,000 ethnic Indians had participated in the November 25 rally which rattled the Malaysian government.
The King's decision to reject the appeals was conveyed in a letter, to the lawyer of one of the detained Hindraf activists by the Malayasian home ministry, Hindraf lawyer Karpal Singh said in a statement on Wednesday.
"The other detainees have received similar letters," he said.
The five detainees are lawyers Uthayakumar Ponnusamy (46), Manoharan Malayalam (46), Kengadharan Ramasamy(40), V Ganabatirau and ex-bank executive Vasantha Kumar Krishnan (34).
Meanwhile, the Malaysian Indian Congress has asked the government to explain how the five Hindraf activists posed a threat to the country's security.
Party's youth wing chief S A Vigneswaran said the detained Hindraf leaders should be released.
"If their detention is simply because of their involvement in street demonstrations, the government should release them immediately. Otherwise, the people should be told what kind of a threat they pose to national security," Vigneswaran was quoted by online media reports as saying.