Although some Muslims have committed acts of terrorism, terrorism is not from Islam and not all terrorists are Muslim.
The Stern Gang was a Jewish Zionist terrorist group that was responsible for many bombings and assassinations, including against British forces in the late 1940's.
The Tamil Tigers are a nationalist terrorist group founded in Sri Lanka who conducted bombings and assassinations, against Muslims and others.
The Irish Republican Army is a Catholic/nationalist terrorist organization, responsible for attacks in Britain and Northern Ireland.
The Ku Klux Klan is an American Christian terrorist organization responsible for the deaths of many non-whites, through bombings, arson, kidnapping, assassination and other methods.
Timothy McVeigh was a non-Muslim American terrorist who bombed a federal building. It is alleged he was an athiest.
The Weather Underground was an American terrorist organization, responsible for bombing the Pentagon and many other targets on American soil in the 60's and 70's.
Anders Behring Breivik is the Norwegian Christian fundamentalist terrorist responsible for the recent massacre in Norway, seeking to turn the society against Muslims.
There are many others, but I think you get the picture. Part of the reason why it may seem to you that Muslims are the only terrorists is due to media exposure. When non-Muslims commit acts of terrorism, they are either shrouded in history or the media makes no mention of their religion or ideology. The fact that this occurs so often is evidence that it is not accidental, rather it is intended to sway public opinion against Islam and Muslims.