Is he bluffing?

[spiff21]

Villain 49/29/1.1 Wtsd 39, Att. to steal 45

Party Poker 10/20 Hold'em (5 handed) pokerhand.org hand converter

Preflop: Hero is BB with A[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/spade.gif[/img].
<font color="#666666">2 folds</font>, <font color="#CC3333">Button raises</font>, <font color="#666666">1 fold</font>, Hero calls.

Flop: (4.50 SB) 5[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Button bets</font>, Hero calls.

Turn: (3.25 BB) 8[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font>, Button calls.

River: (5.25 BB) K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
</font>Hero checks, <font color="#CC3333">Button bets</font>, Hero ..

How often do you call here?