"If we did not buy the rupee would appreciate further," Cabraal said.
The rupee was floated in late March as a 'prior action' ahead of an International Monetary Fund (IMF) loan which has been delayed due to political wrangling.
Following the float of the rupee however, the IMF money has become less important.
Cabraal said Sri Lanka has agreed on a program with the lender and it was now up to the IMF to grant the loan.
He said there was no urgency for the money but it would give comfort to market players who had come to rely on foreign reserves.
The central bank's net foreign reserves fell to 830 million US dollars in March 2009 from a peak of around three billion dollars at the beginning of the crisis in August 2008.
Overnight limits were slashed twice last year as the rupee came under pressure as the central bank attempted to defend a dollar peg.
"We will take this up at the next monetary policy meeting," Governor Cabraal said.
"We have already shown that w