itertools.combinations is in general the fastest way to get combinations from a Python container (if you do in fact want combinations, i.e., arrangements WITHOUT repetitions and independent of order; that's not what your code appears to be doing, but I can't tell whether that's because your code is buggy or because you're using the wrong terminology).
If you want something different than combinations perhaps other iterators in itertools, product or permutations, might serve you better. For example, it looks like your code is roughly the same as:
for val in itertools.product(np.arange(0, 1, 0.1), repeat=6):
print F(val)
All of these iterators yield tuples, not lists or numpy arrays, so if your F is picky about getting specifically a numpy array you'll have to accept the extra overhead of constructing or clearing and re-filling one at each step.