There is no built-in command to do this, mostly because each implementation product model varies, along with the import source format. However, it's pretty easy to roll your own in code.
Check out the ProductImport project in the Active Commerce Training repository, which provides an example of doing just that, in this case, pulling from an xml file.
If you haven't already done so, be sure to check out the other examples located here. This is a good starting point for most common integration points that may be helpful in implementing Active Commerce.