If you are talking to the listing agent, they represent the seller, not you. Therfore they should not tell you what the other offer is, but tell you to submit your best offer. Remember their job is to get the best price for the seller.
If the agent is working for you as a buyer's agent, they must tell you if they know. Their job is to get a house you want at the lowest possible price. They may not know because a good seller's agent would never tell them. Your best action is to have your agent show you what the current market value is on the home you are bidding on, then submit a bid that you would be happy with if it is accepted. Do not overpay for a house by getting caught up in the excitement or emotions of "bidding". Never buy a house that has a higher payment or is more money than you are comfortable paying.