Although the detention and subsequent arrest of the two residents of Brussels, aged 19 and 35 respectively, took place last Thursday, information on the issue was only made public on Monday.
According to the Belgian prosecutors, the two men had a ticket to Greece, but in fact planned to join Islamic State militants in Syria.
Both men were accompanied by a woman, whose husband had already traveled to Syria. The woman was not placed under arrest, Le Soir reported.
The news came amid heightened security in Belgium. The threat of a terrorist attack has increased in Brussels, following a series of deadly attacks in France, where Islamist extremists killed a total of 17 people in three different locations in the Paris area.
Last week, several large-scale anti-terrorism raids were launched in European countries, including Belgium. On Thursday, two suspects were killed and one man was detained during a counter-terrorism raid in eastern Belgium, while on Saturday, Belgian authorities deployed troops alongside police due concerns over a possible terror attack.