The pair are believed to have developed feelings for each other on the set of Friends With Benefits, and Kunis ended her relationship with long-term boyfriend Macaulay Culkin in January, while Timberlake split with Jessica Biel earlier this month.
Kunis is now said to have asked Justin to give her some time before they get together to make sure he is serious.
A source told Now magazine: 'She doesn't want to be seen as a home wrecker. She's into monogamy so she ended it with Macaulay because she was attracted to Justin. But she doesn't want to be another one of his conquests, so she's asked for space. Justin agrees they should wait a while out of respect for Jessica.'