However, he said voters could be influenced by the influx of migrants on the continent, fleeing war in the Middle East and north Africa.
"With... the migration crisis, the short-term impact is for people to think, `Oh Christ, push Europe away from me, it`s bringing me problems`," he told Britain`s Spectator magazine.
"I get the temptation for people to say: look, it`s just one thing after another; surely we`d be better off separating ourselves from this organisation? But I think thatâs the wrong conclusion to draw."
The prime minister suggested that longer-term, voters may conclude it would better to remain close to European policy-making in order to deal with the crisis, hinting that he may not call an early referendum.
Cameron met with Poland Prime Minister Beata Szydlo on Thursday, where he is trying to win support for reforms to welfare payments for migrants within the EU.
Poland is opposed to the reforms, but Cameron said the pair had "agreed to work together to find a solution."
"I want Britain to stay in a reformed European Union, and the prime minister has made clear that Poland wants Britain to remain in the EU," he said.
However, the Polish prime minister told reporters she did not "see eye to eye" with Cameron over welfare and benefits.
Britain has agreed to take in 20,000 refugees from camps in countries bordering Syria, but is not part of the official programme to relocate those arriving independently in Europe.
Germany is keen for European partners to take in more, with official figures showing that it registered 964,574 new asylum seekers in the first 11 months of the year, putting it on course for a million arrivals in 2015.
Britain`s Electoral Commission on Thursday announced that the result of the EU referendum will be declared in Manchester, north west England, rather than London.
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