Yes, there can be a margin requirement when an account holds non-base currencies. IBKR will first determine the Net Liquidation Value of any Non-Base currency balance (expressed in the account's base currency) and determine the haircut rates for each currency pair. Next, IBKR will determine the largest negative currency balance and sort the haircut rates from smallest to largest. Then, starting with the positive Net Liquidation Value (base currency equivalent) with the lowest haircut rate, IBKR will calculate the margin requirement which may be used to offset a negative Net Liquidation Value. IBKR will then repeat this step until all negative Net Liquidation Values have been covered for each non-base currency amount.
Find more information on currency margin calculation in the IBKR Knowledge Base and Forex margin requirements on the IBKR website.