There were no reports of injuries and minimal damage when the homemade bomb went off near the Aisha Mosque and Islamic Center in Walsall on June 21.
The incident came amid heightened religious tensions in the UK over the killing of a British soldier.
West Midlands Police said today that a 25-year-old man and a 22-year-old man have been arrested and are being questioned by counterterrorism police.
The force said police also are carrying out a search and have evacuated some properties as a precaution.