The ruling was made after 97 complaints about the ad for Beats Pill speakers, which features scantily clad women.
The ASA said while it accepted some viewers might find the ad distasteful, it would not cause widespread offence.
However, it ruled the "overall tone" was sexual.
The advert, which is based on the controversial music video for Thicke's song, shows three female models dancing and interacting with the product while dressed in hot pants and crop tops.
It also features one woman kneeling on her hands and knees with a Beats Pill laid on her back.
Those that complained said the commercial was sexist, objectified women and was degrading to women.
Others said it was inappropriate at a time when children would be watching.
In its response, Beats Electronics International said the advert was not intended to be offensive or encourage any inappropriate stereotypes, saying the women were confident, self-assured individuals who were "not subservient to the male character".
It added the dominant images were of the product being used as dumbbells, a hotdog, binoculars and medicine, which were "strong, playful images that most viewers would not see as having any sexual connotation".
In its ruling, the ASA acknowledged some viewers could find elements of the advert distasteful - "particularly the shots of the women's bodies with their heads obscured and the shot of the woman on all fours".
It said as the shots were brief, it did not consider the ad - when taken as a whole - showed any sustained, overtly sexual or provocative behaviour.
However, it concluded the overall tone was sexual and was not suitable for broadcast before 19:30.
The unrated video for Thicke's Blurred Lines - in which the female models appeared topless - was branded misogynistic and banned from YouTube earlier this year.
A second version of the video, featuring the women in the same outfits they wore in the Beats Pill advert, later replaced the original.
An advert featuring singer Robin Thicke performing his number one hit Blurred Lines must not be shown before 19:30 as it is too sexual, the Advertising Standards Authority (ASA) has said.