Watkins is being held on bail of $100,000 cash or $200,000 bond, and is due back in court Friday.
The robbery took place at about 4:30 p.m. Tuesday, police said.
"The 28-year-old male victim went to the home of the defendant . . . to purchase a motorcycle. Once inside, Watkins pulled out a black handgun and demanded money from the victim," police said in a news release.
"The victim handed over U.S. currency and a prescription bottle of oxycodone pills from his pocket. The victim ran out of the house and notified the police," the report said.
Officers from the Fourth Precinct responded, and after Watkins consented to a search, the police found "the victim's proceeds and a black handgun, shotgun and rifle," and Diazepam pills, the police report said.
Watkins also is charged with drug possession and possession of a dangerous weapon.