If you're talking about each segment, it most likely will be the same. If you're talking about the total fare, that is highly unlikely. Unlike airlines, on Amtrak, there is no discount for round trip - the total fare is each segment added together.
Example (to make it easy) - say Boston (BOS) to Washington (WAS) is $100 each way. On Amtrak, the fare would be $200 for BOS-WAS and WAS-BOS. On an airline (assuming the same fare amounts), it may be like $180.