This lamb is standing. John has not let us know that the other three beasts have exited the stage of John’ observations. In fact, as we find out shortly, the 144,000 accompanying the Lamb are on earth, the very domain to which the dragon has been exiled (Revelation 12:9, Revelation 12:12) and where the two beasts operate (Revelation 13:1, Revelation 13:11). But John does not see the lamb running from the beasts; he sees the lamb standing (the Greek indicates continuous standing). It is the posture of victory, of lordship, of dominion.
1 Then I looked, and behold, on Mount Zion stood the Lamb, and with him 144,000 who had his name and his Father’s name written on their foreheads.