A small pipe bomb exploded in front of a building a few blocks from Madison Square Garden early yesterday morning, police said.

The bomb went off at about 1:10 a.m. on a sidewalk in front of the building that houses Studio Dante, a theater at 257 W. 29th St. owned by an actor best known for his role in “The Sopranos,” Michael Imperioli, and his wife, Victoria Imperioli.

No one was hurt, but a cap from the pipe bomb hit and shattered the windows of a van parked nearby, police said.

The explosion was likely not an act of terrorism, Mayor Bloomberg said.

A couple vacationing in New York from Wichita, Kan., Mark and Lisa Schwebke, were staying in the hotel across the street.

“It sounded like ‘kaboom,'” Ms. Schwebke, 51, an emergency room nurse, said.

Mr. Schwebke, 47, a contractor, said that from their window they could see smoke rolling out of the entrance of the theater. “We knew that wasn’t normal,” he said.

The New York Police Department’s bomb squad is investigating the explosion. Police said they did not yet have a suspect.

Pipe bombs are homemade explosive devices typically consisting of a metal water pipe or pipes that are capped and filled with explosive material. The pipe bomb that exploded on West 29th Street yesterday was “low grade,” police said, and had been set in the doorway of the building.

Residents of the apartments in the three floors above Studio Dante were evacuated, police said. The street remained closed until midmorning.

The building’s owner, Mr. Imperioli, played Christopher Moltisanti in the long-running HBO series about a New Jersey mafia family, and has also appeared in such films as “Goodfellas,” “Bad Boys,” “A Shark’s Tale,” and Spike Lee’s “Summer of Sam,” which he co-wrote.

A spokesman for Studio Dante, Darren Molovinsky, said no one was in the theater when the bomb went off. The last show performed there ended in June, and the next one is scheduled to begin in October.

The theater’s interior resembles a 19th century palace; the resident company performs plays by writers who “investigate difficult emotional terrain,” according to its Web site.

Mr. Molovinsky said police questioned the theater owners and employees yesterday, but said they were unaware of who might have planted the explosive device. Their only enemies, he said, are “maybe fictional.”

The last major incident involving explosive devices in Manhattan occurred in 2005, when two grenades detonated on a sidewalk in front of the British Consulate in the middle of the night. Police have yet to arrest anyone in connection with that incident.