I've had this happen to me too, there's enemies in range, but you drop it and it just explodes for no apparent reason!
I do think it's possible that there is stray fire that hits it, or possible some other AoE/explosion that affects it directly or indirectly. It doesn't seem very consistent though. For a period of time I'd say 1 out of every 3 seeker mines I dropped would just explode on me and damage me. I use the cluster version, not sure if that matters, but it wouldn't even split, it would just detonate right after deploying.
For now just remember that and try to throw it more often than you set it down. Otherwise, just be really, REALLY sure nothing else is going on. I've definitely had it blow up on me when behind full cover, no enemy visibility, no AoE or other damage incoming, and no enemies with visibility on me. Even if it can't find a target, it shouldn't detonate and hurt me. But I can't rule out that this has been the problem every time, so like i said just be careful, not too much else we can do for now.
Most times I throw them, but there is moment when I want them to secure my other sides when trying to finish something more important target to make my solo run easier.
And this post was for them who can fix it. I know that players can't do nothing about it. Meaning of this section is to bring these things out. I think.