Zelaya and Robert Micheletti, Honduras' interim president, agreed to the mediated talks after Zelaya met Hillary Clinton, the US secretary of state in Washington, DC.
Zelaya said that he had two specific aims in mind for the talks in Costa Rica.
"What is going to be done is to fulfil the resolution of the Organisation of American States and the resolution of the United Nations, in which they ask first and foremost for the reinstatement of the president of the republic," he said.
"That is number one. Number two is the complete non-recognition of the authorities by coup d'etat, and condemnation of the coup d'etat."
The ousted leader said that the interim government has no legitimacy, pointing to the fact that governments acrss the world have condemned the coup.
"The [interim] government is completely disconnected from all of humanity. All the countries - the Arab countries, the African countries, the Asian countries, the European countries, the countries of the Americas - have all closed their doors to this government," he said.
But while Zelaya has demanded that he be swiftly reinstated as president, the interim government has maintained a tough line against him.
"This isn't a situation that can be resolved in a blink of an eye," Carlos Lopez, designated by Micheletti's interim government as envoy to the United Nations, said in Tegucigalpa, the Honduran capital.
|Zelaya has the weight of interantional support behind him in the run-up to the talks [EPA]
Lopez reiterated the interim government's assertion that the Zelaya would face judicial charges if he returned to Honduras.
Gabriel Elizondo, Al Jazeera's correspondent in the Costa Rican capital San Jose, said Arias has a huge task to fulfil in mediating a solution to the crisis in Honduras.
"To say Arias has a tough job is an understatement. He is basically going to have to do what the OAS and the UN has been able to do, and that is come up with some sort of resolution," he said.
"There are two aspects - one is that the United States has pretty much washed their hands of this and said 'Oscar Arias, you are the man, you mediate this'.
"The second issue is simply the fact the Zelaya has a lot in his favour. I think the coup leaders thought that Zelaya would go away peacefully into the sunset, but he has not. It is to a little bit of Zelaya's credit that things have even got to this point [of mediated talks]."
Zelaya was removed from power on June 28 as he was about to press ahead with a non-binding referendum on the constitution.
His domestic critics said the public vote was aimed at changing the constitution to enable him to run again for office at the end of his current four-year term.
Zelaya attempted to return to Tegucigalpa, the Honduran capital, on Sunday but soldiers and military vehicles blocked the runway and warned off his aircraft.
At least one person among the thousands of people waiting for the aeroplane to land was killed by security forces - the first to die in clashes since the coup.