"Everything is speculation. I think there's likely to be some shifting in the markets," she told reporters at the White House.
The law, also known as "Obamacare," eliminates discriminatory market practices that have imposed higher rates on women and people with medical conditions.
It also limits how much insurers can charge older people. But while the changes are expected to lower costs for women, older beneficiaries and the sick, men and younger, healthier people will likely see higher rates as insurers try to hedge against continued risks.
"Women are going to see some lower costs, some men are going to see some higher costs. It's sort of a one to one shift ... some of the older customers may see a slight decline, and some of the younger ones are going to see a slight increase."
Insurance premiums could rise for some with individual plans, she said, as Obama's Patient Protection and Affordable Care Act enhances the level of coverage and either eliminates or reduces the rate of price discrimination against people who are older, female or have preexisting medical conditions.
"These folks will be moving into a really fully insured product for the first time, so there may be a higher cost associated with getting into that market," Sebelius said.
Sebelius says that the hikes involved will be "slight," but insurance industry representatives have suggested otherwise. And as Reuters notes, a study released this week by the Society of Actuaries projects that on average, individual premiums will rise by 32 percent across the country over the next three years.