Boston Police have closed down Boylston St in the area of the Marathon Finish Line because of two unattended backpacks.
Police have been asking people to avoid the area.
ABC reports that a backpack has been detonated safely by police and there is no indication of danger.
Witnesses tell WBZ-TV that a barefoot man wearing a veil and a backpack was heard screaming "Boston Strong" before police cleared the area.
A video was posted to Instagram that appears to show the man witnesses saw, although that has not been confirmed.
Police say they have a man in custody.
Today is the one-year anniversary of the Boston Marathon bombing, when three people were killed and more than 260 others injured.
This year's marathon takes place on Monday.
In a tweet tonight, police said they are discouraging the use of backpacks at the marathon, "to ease fears and concerns."