The spoof heavy metal band, created by Shearer, Michael McKean and Christopher Guest, shot to fame in mockumentary This Is Spinal Tap in 1984 and went on to record two albums.
The group, whose last album Break The Wind was released in 1992, have confirmed that they are working on a new record.
"It'll be for download as well as on conventional media later this year," Shearer told BBC 5 Live.
After the band briefly reunited for the Live Earth Gig at London's Wembley Stadium in 2007, demand has increased for a proper return.
"We've never recorded the song we did at Live Earth, 'Warmer Than Hell', and I think [Spinal Tap] are trying to revisit their old success," Shearer said.
"Not that they were ever popular, maybe in their own universe.
"We'll do a song called 'Gimme Some More Money', probably with some dubious results."