This transaction could be a pending authorization a merchant has processed from their end.
It does not necessarily mean your account will be billed twice. Certain Merchants, such as internet companies, may authorise a charge when you place an order.
The Merchant may then authorise your Card again when the amount is due. In these instances, the charge may appear twice in Pending Transactions but will be billed to your account only once. Some restaurants will authorize your Card when the Card is put in the terminal.
If you add a tip, the charge may show again with a second authorization but will only be billed once.
If you discover duplicate transactions, please wait to see if they appear on your billing statement. If so, you should contact the merchant to raise a dispute for the transaction.