This isn't quite the usual ko threat, because if Black answers it, White actually loses 3 points. For Black, it's not very useful, because if at , the gain for Black is only 3 points, while the loss would be much higher.
Please correct me if I'm wrong, but it seems to me that more than three points are at stake (Japanese rules are assumed):
You're right; I miscounted.
MrTenuki: 7 points for Black (note that White can get another ko threat by putting the 1-1 stone into atari).
I think it is not a ko threat as the best white can do is to turn the local situation back to seki again. So black can ignore that move of white.