The S&P/TSX composite index fell 32 points to 14,436 at midday, pulled down by lower energy and metals stocks.
The energy sector was down 2.66 per cent, followed by metals and mining stocks, which were 1.35 per cent lower.
The Canadian dollar was down 0.29 of a cent to 85.86 cents US.
The TSX had gained 736 points or 5.36 per cent last week, ending weeks of bad news for stock investors.
Oil prices seemed to stabilize and the Fed reassured markets that it would go slow on raising rates.
But by Monday, oil was on its way downwards again. The West Texas Intermediate contract traded in New York had fallen $1.51 to $55.62 US a barrel and Brent Crude was down $1.07 to $60.30.
In a speech at an energy summit in Abu Dhabi on Sunday, Saudi Petroleum Minister Ali Naimi defended OPEC’s decision at its Nov. 27 meeting to keep its production levels unchanged.
“As a policy for OPEC, and I convinced OPEC of this, even Mr al-Badri (the OPEC secretary general) is now convinced, it is not in the interest of OPEC producers to cut their production, whatever the price is," Naimi was quoted as saying.
"Whether it goes down to $20, $40, $50, $60, it is irrelevant," he said, saying oil will not soon rise to $100 a barrel level.
Naimi said low prices might stimulate the world economy and denied OPEC is trying to push other producers, including U.S. shale producers, out of the market.
Oil hit $107 a barrel in June, but has plunged nearly 50 per cent since then due to low demand and stalled global growth.
The U.S. markets continued to rally, which saw the Dow rise by three per cent last week.
The Dow was up 79 points to 17,884, the S&P 500 was almost unchanged at 2070 and the Nasdaq edged up three points to 4768.