The comments were written sometime between 2:45 a.m. and 3:15 a.m. Wednesday in a tunnel designated for free speech.
N.C. State police Capt. Jon Barnwell said someone used spray paint to write comments about Obama that bordered on threatening.
"Kill that N_____" and "Shoot Obama" were among two things written on the campus tunnel.
The Free Expression Tunnel was built in 1939 to allow people to express their first-amendment rights.
Barnwell said someone noticed the writing before classes began Wednesday.
N.C. State officials responded by painting the tunnel white, saying the negative expressions had gone over the edge of what was acceptable.
Campus police worked with the secret service and identified four people believed to be responsible. Those people were interviewed.
NC State police say the people who wrote the racist comment in the tunnel are students.
It was then determined that the graffiti was not criminal as there was no serious physical threat to Obama.