Police Chief David Kimaiyo said that at least 200 of the arrested are sympathizers of the Islamist militant group and al-Qaida affiliate, al-Shabaab. The rest of the arrested are still being processed.
The 627 individuals were taken into custody in the mainly Somali neighborhood of Eastleigh, also known as "Little Mogadishu," and the site of the explosions.
The attacks, which killed six people, were launched at rush hour, and targeted a clinic and two small restaurants.
Interior Minister Joseph Ole Lenku called the "barbaric" attack an "act of cowardice perpetrated against innocent and peace-loving Kenyans who were going about their normal activities ..."
BBC's Caroline Karobia noted that mass arrests are common in Kenya after such attacks.
No one has yet claimed responsibility for the bombings.