Animal Aid accused the broadcaster of "continuing its grotesque cover-up of horse deaths at the Grand National meeting".
The charity was commenting as it prepared to protest outside Aintree in the lead-up to this weekend's Grand National Steeplechase.
On Friday, the second day of the three-day meeting, three horses perished.
Two of the victims broke their necks or backs almost simultaneously at Valentine's Brook on the Grand National course, while pitted against 27 other horses in the Topham Chase.
They were eight-year-old Prudent Honour and seven-year-old Plaisir D'Estraval. Neither had run over the Grand National fences before, the group said.
The third casualty was Schindlers Hunt, who was reported to have broken a front leg during the John Smith Melling Chase, just 35 minutes earlier.
The first day of the meeting also produced a casualty. A six-year-old mare, Pagan Starprincess, fell at the first obstacle in the 22-runner Silver Cross Handicap Hurdle. She is believed to have suffered fatal spinal injuries.
Animal Aid said it feared that Saturday's seven races, including the Grand National Steeplechase, would see the current tally of four deaths for the 2010 meeting increase further.
Last year, five horses were killed at the three-day event.
Earlier this week, Animal Aid director Andrew Tyler wrote to BBC head of sport Barbara Slater demanding that deaths at Aintree are not in future "glossed over" by its television team.
He accused the BBC of "fashioning a dishonest, sanitised picture of the Aintree meeting to maximise its earning potential".
The BBC distributes footage of the Grand National to more than 140 countries and a worldwide audience of more than 600 million.
"The BBC seems to think that it can dispose of the deaths of three horses in the space of 35 minutes, in three or four hastily-uttered sentences.
"The publicly funded broadcaster might profit handsomely from marketing its Aintree footage but that is no excuse for its execrable performance."