Najib was ousted in an election in May last year amid public fury over the alleged theft of $4.5 billion from 1Malaysia Development Berhad (1MDB), Presstv Reported.
He has pleaded not guilty to ten charges of criminal breach of trust, money laundering and abuse of power and his trial was originally set to begin on Tuesday.
His lawyers, however, filed an application last week to stay the trial pending an appeal over a lower court's ruling to transfer some of the charges to Kuala Lumpur High Court, media reported.
Harvinderjit Singh, one of Najib's lawyers, told Reuters in a brief text message that the Court of Appeal had agreed to postpone the trial "until the appeal is heard."
No new date for the trial or the appeal has been set, he said.
The postponement is seen as a blow for the government of Mahathir Mohamad, which reopened probes into 1MDB shortly after the election and had promised to bring those involved in the scandal swiftly to justice.
Prosecutor V. Sithambaram told Reuters he expected the appeal to take only a week or two.
"It's just a hiccup," he said. "The case is just delayed slightly."
The charges against Najib relate to a suspected transfer of 42 million ringgit ($10.3 million) into Najib's bank account from SRC International, a former 1MDB unit.
The trial is the first of four criminal proceedings that Najib is expected to face over the 1MDB scandal so far, and the sum involved is a fraction of the $1 billion that investigators say allegedly made their way into his bank accounts.
Police found nearly $300 million worth of goods and cash at properties linked to Najib soon after the election.
Authorities have also charged his wife, Rosmah Mansor, and several high-ranked officials of the former administration. All of them have pleaded not guilty.
Najib has consistently denied wrongdoing and says the charges against him are politically-motivated.
In recent weeks, he has undergone a public makeover, appearing in a music video portraying himself as a champion of the working class and throwing jibes at the ruling government on social media in a bid to shed the image of a wealthy, elite politician.
But the charm offensive may not help him in court. Najib faces years in prison after being hit with a total of 42 criminal charges, most of them linked to 1MDB.
At least six countries, including the United States, Switzerland and Singapore, have launched money laundering and graft probes into 1MDB, set up by Najib in 2009.
US prosecutors say money stolen from 1MDB was used to buy a private jet, luxury real estate, artwork by Picasso and Monet, as well as jewelry for Rosmah.