But only 12 per cent of respondents mentioned sex with no prompting in the 1997 survey.
When asked if there was too much sex on television - 38 per cent of respondents agreed there was in 1998, compared with 32 per cent in 1997.
Of those quizzed, 55 per cent said there was the right amount of sex on television, compared with 62 per cent in 1997.
But the BSC said there was no evidence to support the perception of increased sexual activity in its content analysis.
The survey was carried out in November 1998, a time when an unusual number of sex-related programmes were on the air as well as extensive coverage of the relationship between US president Clinton and Monica Lewinsky.
TV violence remained the most worrying issue for viewers, but the number of people mentioning it as a concern has decreased to 32 per cent from 46 per cent in 1997.
According to the BSC's content analysis the number of primetime terrestrial shows containing violent scenes has fallen to 43 per cent in 1998, compared with 52 per cent in 1993.
BSC director Stephen Whittle told Broadcast: 'It's up to broadcasters to take note of what this research tells them; viewers are saying that sex and bad language are far less justifiable in context than violence.'
The BSC said that in 1998, 18 per cent of terrestrial television programmes depicted sexual activity against 40 per cent on satellite TV.
Programmes that recently came under fire for sexual content include Channel 5's Sex and Shopping and LWT's Vice: The Sex Trade. However, the report stated that most scenes of sexual activity on terrestrial television occur in films (29 per cent), drama (22 per cent) and soaps (20 per cent).