The Prime Minister suggested the UK could be forced to withdraw from the convention to ensure foreign criminals are deported.
His comments come as his party conference shadow boxes the anti-European Ukip, which poses a significant challenge in many Tory-held constituencies.
Ukip will not be mentioned from the conference stage, as part of a plan to deny the party the oxygen of publicity, but the strategy looks likely to fail, with Ukip leader Nigel Farage due to speak at three fringe meetings today.
An analysis published yesterday also suggested donors were deserting the Tory party for their anti-European rivals
The convention is enshrined in British law but is despised by many on the Conservative right. Some have called for the UK to withdraw from it completely.
"That may be where we end up", Mr Cameron said.
The ECHR, which includes provisions including the right to a family life, has been cited by criminals to argue that they should be allowed to stay in the UK. It is enshrined in law through the Human Rights Act.
Mr Cameron said: "I think what we need to do is look and think about the outcome we want. I'm less interested in which convention we're signed up to. As Prime Minister, what I want to know is can I keep our country safe."