About 200 people had been evacuated from The Mall shopping center after an unknown person called local media outlets to warn them about the bomb an hour ahead of time, the Greek website Newsit reported.
"We have placed a bomb in the mall and it will explode," a caller warned, giving the location of the bomb -- in a garbage bin -- inside the shopping center.
Two security guards were slightly injured in the explosion and were taken to the hospital, GreekReporter.com reported.
The bomb caused extensive damage to the building, Newsit.com reported.
Police said the bombing may be related to a recent spate of politically motivated attacks against austerity measures that last week saw gunmen shooting at the New Democracy building where Prime Minister Antonis Samaras has an office.
At least 17 bombs were set off earlier this month at several New Democracy, Panhellenic Socialist Movement and Coalition of the Radical Left buildings, authorities said.
A group called the Militant Minority, a suspected left-wing anarchist organization, claimed responsibility last week for attacks on the homes of five journalists, ekathimerini.com reported.