Police were looking for a 39-year-old man reported missing hours earlier when they went to the property at Glenorie, on Sydney's northwest outskirts, about 11.30am on Friday.
NSW Police Detective Superintendent Naomi Moore said officers discovered what they believed were human remains partially buried in a paddock.
"It is covered by some items at the moment, which is what's limiting us from being able to confirm that it is human remains," she said.
The man was reported missing by family about 9pm on Thursday, Det Supt Moore said.
"It is possible that he had been missing for a couple of days," she said.
Two men and a woman aged in their 20s and 30s were arrested at a nearby home but none have been charged as yet.
"We believe they were known (to the man reported missing) and do have some further information that they can offer to our investigation," Det Supt Moore said.
The discovery is being treated as suspicious and homicide detectives are involved in the investigation.
The paddock had been declared a crime scene along with the nearby home of the three people in custody, Det Supt Moore said.
"I expect that this will be something that will take a lot of our resources over the next three to four days, if not longer, as we really try and piece together what's occurred," Det Supt Moore said.
