The suspects were arrested on March 22 ahead of a series of deadly terrorist attacks on an international airport and a subway station in the Belgian capital Brussels.
According to the Focus, police in the southern German state of Bavaria arrested the three men after receiving a relevant intelligence tip-off.
"Investigations have been launched into the suspected planning of a serious criminal act against the state because there was notification of that," a police spokesperson said.
The spokesperson also said that thus far there has been no indication that the suspects had any links to the Brussels attacks even though this could not be excluded.
On Tuesday, at least 31 people were killed and 270 more injured in two bomb blasts in Brussels Airport and an explosion at the Maalbeek metro station in central Brussels. The country's security level has been raised to maximum following the attacks.