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Yes it is, looks like it's a MM wandering for a female.

I found him roaming around while searching for Desert night lizards, I couldn't help leaving him next to a busy highway. Is it OK to keep him in captivity? I have a rose haired tarantula. Is it the same kind of care for this specific kind of tarantula?

@jbelectric Basically same care, but I'd let him go. He's not going to live long, nor eat a lot, all that's on his mind is finding a mate. Maybe try locating a female burrow and let him go near it. Might see some courtship.

I'd love to live somewhere where t's are wandering around
Can't say anything about care since I don't know what exactly he is, but if he's a mature male I'd let him get back to duty since he won't live very long anyways. Also, there's lots of reputable breeders you can buy t's from

How can I know for sure if he is a mm.
He isn't that big to be honest with you.
Maybe 1.5" long. Or 1.25".

you could do a quick search on tibial hooks (some species don't have those) or boxing gloves. Only mm have them.

@jbelectric Often the males are much smaller than females are. This is the time of year for tarantula males to go searching for females and it would be extremely rare to find a female just wandering around. Females tend to stick very close to home, but males will travel great distances in search of them.

As others have said, this is almost certainly a mature male based on both its dimensions and the fact that you found it wandering about. Males are almost always smaller than females of the same species -- at least in body size; they have proportionately longer legs and smaller abdomens. Where did you find the tarantula? Several species are not that large as adults and knowing where you found this one would help in determining species, whether it is indeed a mature male and how best to keep it if you decide to do so (although, as others have said, I would recommend releasing it somewhere safe near where it was found since mature males do not live long and are rather sad to see them in captivity, always trying to escape).