The 250-kilogram (550-pound) dud explosive was found Wednesday evening during construction works in the northern district of the city, AFP reported.
A one-kilometer radius was sealed off, and several roads blocked, including two highways, city authorities said, warning that this could affect traffic to the airport.
A hotel with 250 guests was also evacuated, with the bomb expected to be defused in the early afternoon.
More than 70 years after the end of the war, unexploded bombs are regularly found buried in German soil, a legacy of the Allies' intense bombing campaigns against Nazi Germany.
Authorities estimate that some 3,000 unexploded bombs remain underground in Berlin alone.
Last Christmas, 54,000 people were evacuated from southern Germany's Augsburg city, after the discovery of a 1.8-tonne WWII-era unexploded bomb.