Barcelona said on their website that the Porto playmaker would arrive in the city on Monday and would undergo a routine medical on Tuesday prior to signing the deal.
The Spanish sports media said Barca were prepared to pay Porto 12 million euros ($14.75 million) and exchange Portuguese winger Ricardo Quaresma for the Brazilian-born 26-year-old.
Earlier Barcelona president Joan Laporta told Barcelona-based sports daily El Mundo Deportivo that he was confident of closing the deal.
"We only have to tie up the final details of the agreement," he said. "I'm quite optimistic and believe that Deco will end up becoming a Barcelona player."
Laporta said the possible inclusion of Quaresma in the deal was one of the details yet to be finalised.
Deco played in Portugal's 1-0 defeat by Greece in the final of Euro 2004 on Sunday.
As well as playing a crucial role in Portugal's run to the final, Deco also inspired Porto to victory in the Champions League, earning the man of the match award in their 3-0 victory over Monaco in Gelsenkirchen in May.
At the same time Laporta said he did not think Dutch midfielder Edgar Davids would remain with the Catalans.
"I don't believe that Davids will play for Barcelona next season," said the Barca president. "We are looking for another player that has his sort of defensive characteristics."
Davids, who was part of the Dutch squad that reached the Euro 2004 semi-finals, joined Barca on loan from Juventus midway through last season.
He played an important part in their late season renaissance that catapulted the team to second place.
The midfielder is a free agent after completing his contract with Juventus.
