Steven Tyler was reportedly “surprised” by his subdued birthday celebrations.

The Aerosmith rocker turned 66 years old on March 26, and he honoured the milestone by accepting an award at the National Music Publishers' Association Celebration of the American Songwriters in Washington D.C. on Tuesday.

Steven was acknowledged in Capitol Hill for the campaigning work he has done for songwriters’ rights over the years, and he was also presented with a special cake.

"Steven was really surprised," a source told People magazine of the rock star’s reaction when he saw his face painted in frosting on the piano shaped dessert. "He was not expecting it."

The star then performed several hits for partygoers.

Democratic representative John Conyers of Michigan joined Steven onstage while he sang Walk This Way, and apparently the musician showed the politician some dance moves.

"Steven was teaching him how to walk this way," an onlooker revealed.

It is rumoured the star isn’t bothered at all about getting older, as turning 66 isn’t significant for him.

“For Steven, age is just a number. He doesn't think about his age," a friend told the publication.

Although he has been active in the activist sphere for many years, Steven previously revealed he thinks big brother probably exists.

The rocker doesn’t believe people should dismiss the idea they are being spied on by the powers that be.

"Yeah, I have. I always thought that once they invented credit cards and so forth, that there was a whole hidden agenda. You can either be naïve and not think so, or you can smarten up and know that there is," he explained to The Cut.

"And once there’s a thing called the Internet, of course it can get tapped into. It just can. I always knew it could, so."