Stafford Police Department officers responded to shots fired in the 3900 block of South Main Street at about 1:48 p.m. on Friday.
When they arrived, police said they discovered the off-duty officer was working an extra detail with FedEx when he observed a robbery.
Police said that in hopes of preventing the robbery, the HPD officer engaged with the suspected robbers and discharged his firearm.
Stafford PD said there were at least two suspects in the theft but said it could be more.
Officials don't have a complete description of the suspects but said one was wearing a ski mask.
It is unknown how many shots were fired or what the suspects intended to rob.
No one is believed to be injured as a result of the shooting.
This is an ongoing investigation.