Two men threw an inactive grenade that did not explode towards troops who arrived at the scene after the suspects crossed the fence from the Hamas-run coastal enclave.
The attack took place in front of a building where Islamist militants gunned down employees of Charlie Hebdo in 2015 because of the republication of cartoons depicting Prophet Mohammad.
The 38-year-old said he grabbed the narwhal tusk that was mounted on a wall while another man used a wooden chair to fend off the attacker.
No one was hurt in the incident last week in Koekelberg, a northwestern neighborhood of the Belgian capital.
Attempts to gain access to synagogues, which are restricted to worshipers for security reasons, are common in Antwerp. But such attempts by men carrying knives are extremely rare.
The arrest comes a day after a stabbing attack in Jerusalem, making this the third incident invloving a knife in twenty-four hours.
The Palestinian drew the knife as the police seized and brought to her arrest.