Unknown. And it depends a bit on what you mean by alone. We've had a pretty good look at the local area as it were and haven't discovered any other races broadcasting their location. That bodes ill for finding anything nearby anytime soon. But the universe is so big, it would be crazy to rule it out.
@sigfried I mean by “alien alone”
well that depends on your definition of alien. are there liforms off earth? yes microorginisms and signs of wich have been found off planet. wether or not there is intelligent life off earth is debateable.
@madix and i mean intelligent life forms
I hope not. As the old saying goes, if we are, "seems like an awful waste of space."