Is it ok to post an abstract of a conference paper... which I will be presenting in a conference scheduled 3 months from now... on ResearchGate?
Ultimately, only the conference organisers can tell you whether posting the abstract is acceptable, but it is very unlikely that they would object. It's now fairly normal for academics to have their own websites on which they post the abstracts of all their papers, presentations etc, with links to the published versions. I have never heard of a publisher or conference organiser objecting to the posting of abstracts (rather than full papers) in this way, but academia is a diverse environment and it's always possible that there is an exception out there.
Some of the big conference organisers have published policies on this (the IEEE policy is an example), so if the conference is organised by a large organisation then it may be worth searching online. Otherwise, just email the conference organisers.
One other thing to find out is whether you can post the submitted version of the whole conference paper on a pre-print server or your own website. Doing this makes your work more accessible to a wider audience, and is allowed by many large conference organisers (see the IEEE policy linked above, for example). If you're not familiar with the benefits of pre-prints or the process for posting one, there is a useful guide in Nature Index.