Baltimore mayor Stephanie Rawlings-Blake had a large cup of water thrown on her Saturday at a community event at the mall where violence erupted in the city in April.
Police have arrested Lacheisa Pailin-Sheffer, 37, of Baltimore and charged her with second-degree assault.
The mayor was unhurt, her press adviser told WBAL-TV in Baltimore.
"I didn't know what it was that she threw at me," Rawlings-Blake told the Baltimore Sun after the incident. "I hope it was water. It was more shocking than anything else."
Rawlings-Blake was attending the Mondawmin Festival, a community event that promised "free food, art, basketball, obstacle course, and over 60 non-profit and agency booths offering resources direct to residents," according to the events listing on the City of Baltimore's web page.
In April, people took to the streets in Baltimore to protest the death of Freddie Gray in police custody. On April 27, the protests grew violent in the neighborhood near Mondawmin Mall.
The protests erupted into riots and looting that led the state of Maryland to declare martial law in the city.