The figures are the first indication of the central bank's currency holdings after it stunned financial markets by scrapping the more than three-year-old cap last month, a policy it later said would have cost 100 billion francs ($108.68 billion) to defend in January alone.
The SNB held 498.398 billion francs ($541.5 billion) in foreign currency at the end of January, compared with a revised 495.130 billion francs in December. The December figure was revised from a preliminary estimate of 495.104 billion.
Foreign exchange reserves, which are reported in francs but held in euros and other currencies, would have been worth much less since a surge in the Swiss currency following the removal of the cap against the euro on Jan. 15.
The fact that reserves rose last month therefore indicates that the central bank may still be intervening to rein in the franc even though it is no longer pegged to the single currency.
A spokesman for the SNB declined to comment on possible interventions in foreign exchange markets.
Intervention by the SNB to maintain the cap pushed foreign exchange reserves to record high levels, equivalent to around three quarters of Swiss gross domestic product.
A weekly rise in the cash commercial banks hold with the central bank is a further sign that the SNB has intervened to weaken the franc since ditching the cap.