Police said officers responded around 6:20 p.m. to reports of a robbery at an apartment complex in the 500 block of Lighthouse Drive.
The victims reported that they were entering their apartment when a man they had noticed loitering in the parking lot approached.
Police said the man pointed a five-inch folding knife at the pair, held it against one victim's neck and demanded money.
The man forced the two into their apartment at knifepoint, demanded a wallet from one of the victims and searched the other victim's purse, according to police.
Neither victim was injured.
The suspect then fled on foot through the parking lot.
Police said he is described as a black man in his 50s who is roughly 5 feet 7 inches tall and weighs about 150 pounds. He was wearing a gray hooded sweatshirt and black pants at the time of the robbery.
Police said officers were told that the suspect has been seen in the apartment complex in the past.
Anyone with information about the robbery is encouraged to call Vallejo police at (800) 488-9383. Those who wish to remain anonymous may call the Solano Crime Stoppers tip line at (707) 644-STOP.
Cash rewards are offered for phone tips that help solve violent or serious crimes.