One in three people do not realise that discriminating against colleagues with HIV is illegal, a survey by the National AIDS Trust and pollsters Mori revealed.
Only 65% of the 2,048 adults questioned were aware that it was against the law to discriminate against someone with HIV at work, contravening the Disability Discrimination Act (DDA).
About 40% also said they would feel uncomfortable working with someone with the disease.
But attitudes towards people with HIV have improved over the past few years, the survey suggests.
About 57% of respondents polled in 2000 said that people who had been infected with HIV only had themselves to blame, compared with 44% in 2005.
Deborah Jack, chief executive of the National AIDS Trust said: "The Disability Discrimination Act requires all employers not to discriminate against people living with HIV. This survey shows that the majority of people have supportive attitudes to HIV positive colleagues in the workplace.
"But it also reveals continuing high levels of ignorance which must be addressed through workplace HIV policies and training."
A small number (7%) also said that people with HIV did not deserve the same kind of support as people with cancer.