The bones were found near Junction 9 of the motorway in Wednesbury on Monday evening.
It is not yet known whose the remains are or how long ago the person died but officers suspect they have been in the dense woodland "for some time".
Forensic officers were seen searching an embankment on the Wednesbury side of Junction 9, close to a railway line and the River Tame.
The woodland being searched by police is in between the motorway and Axeltree Way, around 100 yards away from KFC and Pizza Hut and half a mile away from IKEA.
It is not yet clear how the remains were found, with West Midlands Police unable to confirm whether they were discovered by a member of the public.
An investigation is underway and detectives were seen examining the woodland on Monday.
Meanwhile the bones are being examined in a bid to identify the person and the cause of their death.
A spokesman for West Midlands Police said: "We are investigating after human remains were found in Axeltree Way, Wednesbury yesterday evening.
"The remains appear to have been there for some time and tests are being carried out to identify the victim and establish the cause of death.
"Anyone with information should contact us quoting log 3826 of 12/4."
Remains have been found left in undergrowth next to major West Midland motorways at least twice before in recent years.
In 2015 remains belonging to Oldbury man Surjit Takhar were found close to the M54 seven years after he disappeared.
And in 2010 remains were found in undergrowth on an embankment near Junction 2 of the M5 in Oldbury.