Starring Benedict Cumberbatch and Martin Freeman, the modern-day adaptation of Sir Arthur Conan Doyle's 1891 Sherlock Holmes short story A Scandal in Belgravia aired on New Year's Day.
The episode feature actress Laura Pulver wearing just diamond earrings and high heels at one point as she played dominatrix Irene Adler.
In the scene, shown 25 minutes before the 9pm watershed, Pulver's modesty was covered by some clever editing, but the character was still sexually suggestive, stroking Sherlock's face at one point with a riding crop.
She also wore just a thong in another scene as she entered a room with a woman tied to a bed, and tampered with Sherlock's mobile phone so that text messages would be announced with a sexual moan.
Nearly 10 million people tuned in to watch the New Year's Day episode, but some viewers have complained about the racy scenes being shown pre-watershed, reports the Daily Mail.
One viewer wrote on Twitter: "Dominatrix?! Watershed anyone? My ten year-old was watching that."
Another viewer tweeted: "I don't think the storyline in Sherlock is pre-watershed suitable."
A third wrote: "How was Sherlock on pre-watershed with that slut walking round with no clothes on for most of it?!"
The BBC responded by defending Sherlock and insisting that it had not received any complaints.
A spokesman for the corporation said: "We're delighted with the critical and audience response to the first episode, which has been extremely positive, and have received no complaints at this stage."
It is not clear if any viewers have complained to media regulator Ofcom about the scheduling of A Scandal in Belgravia.
The show's co-creator Steven Moffat had previously said that the racy Adler was introduced as Holmes's latest foe in order to offset the gay undercurrent between him and his sidekick Dr Watson.
Sherlock's return had been largely well received by viewers, although some Twitter users complained about the frequent references to a "cameraphone" by the characters, rather than just saying smartphone as people typically do.
> Sherlock Lara Pulver: 'Nude scenes made me feel vulnerable'