No. Two different populations of players. After you play the same number of games on both sites, you could compare them to get an idea of how closely they're rated.
yahoo ratings vs. chess.com ratings...
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I have a higher rating on chess.com live chess than yahoo. I don't know why. 
Apr 30, 2009
0
#4
Yahoo is not a chess site. Yahoo's format is designed to encourage csual games, but discourage serious chess players. Moreover, there is no reliable anti-engine monitoring at Yahoo.
Look at Edward Collin's comparisons. These are a decade old, but the only change needed to update is that the servers have gotten much better, while Yahoo continues to revel in its mediocrity.
Apr 30, 2009
0
#5
Ziryab wrote:
Look at Edward Collin's comparisons. These are a decade old, but the only change needed to update is that the servers have gotten much better, while Yahoo continues to revel in its mediocrity.
That comparison chart does not judge Live Chess very positively. 
...are they roughly equivalent?