The Paris Champ de Mars park, which surrounds the Eiffel Tower, was closed off after the bag was found.
Pictures published by French media showed a blue bag containing a number of different ammunition types.
Subway lines around the Arc de Triomphe were also evacuated.
Footage posted to social media showed people running up escalators at the Charles-de-Gaulle Etoile metro station following the evacuation order.
The Eiffel Tower was evacuated on Tuesday afternoon
Traffic had returned to normal by 4.30pm according to French police.
France is on a heightened terror alert following the beheading earlier this month of Samuel Paty, a teacher who showed his students cartoons of the Muslim prophet Muhammed as part of a class on freedom of expression.
His attacker, 18-year-old asylum seeker Abdullakh Anzorov, had reportedly been in contact with a jihadi fighter in Syria.
Abdullakh was later shot dead during a confrontation with police.
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Emmanuel Macron by the coffin of Samuel Paty
Seven other people, including two schoolchildren, have been charged with terror offences in relation to the attack.
Mr Paty was posthumously awarded the Légion d’honneur, the highest French honour.
Following the killing, and the republication of cartoons in defiance, Turkish President Recep Tayyip Erdogan called for a boycott of French products.
He sensationally claimed “there is oppression against Muslims in France”.
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France is on a heightened terror alert
President Emmanuel Macron hit back vowing to defend secularism and stating France “will not give up our cartoons”.
In 2015 12 people were killed during a terrorist attack on the offices of Charlie Hebdo, a satirical magazine which had previously published Muhammed cartoons.
Last month two people were wounded in an attack outside the former offices after the cartoons were republished.