Safe...ish. Computers these days aren't as prone to be wiped out with a magnet as the disc of yore (unless you're talking about HUGE magnetic fields, in which case you're probably going to fry anything Electronic anyway). However, magnets can still affect your tablet's performance if there's a sensor nearby or if the magnetic field interferes with something else, like the display connector or input devices (for instance, S-Pen is known to be affected by misaligned magnets if placed near the Wacom circuitry).