Does the same file transfer speed occur with a wired connection? Please understand that Mbps (Mega bits per second) is NOT the same as MB/s (Mega bytes per second).
Based on what you say this would not add up however if the transfer rate was in bytes then this would be normal. When doing the file transfer are you downloading from the internet or transferring the file between two machines on your network? Transferring data between two machines on your network should give you a better understanding of what the speed of your wireless connection is.
8 bits in a byte
1024 bytes in a Kilobytes
1024 Kilobytes in a Megabyte
1024 Megabytes in a Gigabyte
2 Mbps = 2000 Kilobits per second
2000 / 8 = 250 Kilobytes per second transfer rate
(Where / is a divide)
Hope This Helps,