The sexual behavior of individuals living with HIV determines the onward transmission of HIV. With the understanding that antiretroviral therapy (ART) prevents transmission of HIV, the sexual behaviors of the individuals not on ART with unsuppressed viral loads becomes of the greatest importance in elucidating transmission. We assessed the association between being on ART and sexual risk behavior among those living with HIV in a nationally representative population-based cross-sectional survey of households in South Africa that was conducted in 2012. Of 2237 adults (aged 15-49) who tested HIV-seropositive, 667 (29.8 %) had detectable antiretroviral drugs in their blood specimens. Among males, 77.7 % of those on ART reported having had sex in the past year contrasted with 88.4 % of those not on ART (p = 0.001); among females, 72.2 % of those on ART reported having had sex in the past year while 80.3 % of those not on ART did (p < 0.001). For males and females, the odds of reporting consistent condom use and condom use at last sex were statistically significantly higher for individuals on ART compared to those not on ART (males: consistent condom use aOR 2.8, 95 % CI 1.6-4.9, condom use at last sex aOR 2.6, 95 % CI 1.5-4.6; females: consistent condom use aOR 2.3, 95 % CI 1.7-3.1, condom use at last sex aOR 2.3, 95 % CI 1.7-3.1), while there were no statistically significant differences in odds of reporting multiple sexual partners in the past year. In this nationally representative population-based survey of South African adults, we found evidence of less risky sexual risk behavior among people living with HIV on ART compared to those not on ART.