Hello kousantz,
best/easiest application i've found is startup disc creator in your menu on mint 14. If the usb is plugged in the program will show it listed in the bottom half of the dialogue box on screen, (ignore the top part about iso's) just click on erase disc, say yes to are you sure and enter your pass if this is required, the usb should be done in seconds.
There's other ways and app's in package manager/software centre but this is just my favourite

Lenovo ThinkPad T61 Linux Mint 12 Lisa & Mint 14 Nadia (on different HDDs) 2x Intel Core 2 Duo CPU T7500 @ 2.2GHz/ Kernel Linux 3.0.0-12-generic (i686) Desktop Environment - Cinammon 1.6/ Intel GM965/GL960 Graphics Controller.