Citing two people familiar with the matter, The Wall Street Journal said people who have managed to navigate the problem-plagued website and have signed up for an insurance policy represent a fraction of the government's goal of 500,000 enrolled in October.
The ACA, seen as the centerpiece of President Barack Obama's domestic agenda, offers insurance exchanges administrated by the federal government and by some states where millions of people without health insurance can choose a policy at an affordable price.
The low number of those who have enrolled worries the promoters and defenders of "Obamacare", because the plan's success depends on a large number of people signing up and thereby lowering the individual cost.
The government expects that some 7 million people will obtain health insurance coverage by the end of March.
The department of health and human services told Congress last week that it will release the first enrolment figures this week.