The first muntjac deer were brought to the UK from China in the 20th century
The Nottinghamshire Wildlife Trust have had a number of calls about deer sightings in the east of the city.
Deer have been spotted near Green's Mill, in Sneinton, along Nottingham canal and even on Notts County's pitch.
Erin McDaid, from the Trust, said: "The deer population is growing across the UK and as they're territorial they're moving into suburbs and urban areas."
The sightings appear to be of muntjac deer which are small enough to live in disused buildings or railway cuttings.
Muntjac are a non-native species whose numbers in England have increased since some were released from Woburn Park, Bedfordshire, in 1925.
BBC Nottingham's security guard Keith Walker even spotted one of them in the car park.
"I thought it was a dog at first," said Keith. "I looked again and I couldn't believe my eyes, it was a deer."
Erin has a theory about the increase in sightings.
He said: "There's more forestry, there are more trees, and the Notts Wildlife Trust and local authorities are trying to create more green space around our city to improve our quality of life.
"Obviously that does provide more places for all manner of wildlife to live including deer."
However, there is one problem, particularly with muntjac, as Erin explained.
"When they come into the city they might be coming into conflict with people because they might be eating prize petunias or garden plants!"
Nottinghamshire Wildlife Trust encourage the public to get in touch if they have seen something out of the ordinary. If you have spotted a deer in an urban area contact them on 0115 958 8242.