There are fears that thousands of migrants from Romania and Bulgaria could arrive in the UK next year once transitional arrangements set up when the two countries joined the EU in 2007 come to an end.
Speaking to Andrew Marr on the BBC today, Cameron said ministers would now look at making it harder for migrants from the EU to come to Britain and claim benefits or access free health care on the NHS.
Cameron said: "Clearly, one of the key reasons for being a member of the European Union are what are called the key freedoms - the movement of goods, the movement of services, the movement of people.
"There are restrictions already on the movement of people if you have, for instance, an emergency. Should we look at arguments about should it be harder for people to come and live in Britain and claim benefits?
"Yes, frankly, we should - so there are areas even in the free movement of people where we might want to make changes.
"We have got this balance of competencies review but all of these areas should be carefully looked at."
Speaking ahead of a key speech later this month in which he will outline his stance on Europe, Cameron said that voters will be offered a "real choice" about the UK's membership of the EU.
But there would be no in-out referendum, which has been demanded by senior eurosceptic Tories and the UK Independence Party (Ukip).