OFDM signal spectrum


I was just testing the transmission of an OFDM signal through an URSP2
and using another USRP2 to receive it.

I noticed that a carrier was present in the OFDM signal’s FFT. Is it
to be this way for OFDM? I mean, when we put a signal on the RF we are
just changing its center frequency, not inserting a carrier. I

I would be grateful if you clarified this for me


The carrier is not present in the transmitter before sending the signal
to the USRP2. But in the receiver, in the base band, the signal has this
DC component in its spectrum. Is this a carrier introduced by the USRP2
when sending the information or is this the way it is supposed to be
when sending OFDM signals? I’ve never heard about introducing a carrier
in the OFDM signals…