The institute said that exports to European Union countries that represent Portugal's main market rose by 3.1 percent while imports from those countries rose 3.9 percent.
Export growth had driven Portugal's economic recovery that began in the second quarter of last year after a long recession - the worst since the 1970s - due to the country's debt crisis and tough austerity measures implemented under an international bailout that Lisbon exited in May.
But internal demand started is now growing as the country heads toward its first year of economic growth in 2014 after several years of slump.
The government expects economic growth this year to reach 1 percent.