Halifax go into the match four points clear at the top of the National League, and unbeaten in their last seven games.
"I've got fond memories of the FA Trophy," said the Town keeper.
"That might be my only game at Wembley, hopefully not.
"The lads want to get there.
"Obviously we only have to win a few more games and we're there.
"Again, it's about momentum, we don't want to take our foot off the pedal, we want to keep the wins rolling."
Johnson will be up against his former Halifax boss Billy Heath, who is in charge at Alfreton.
"I haven't got one bad word to say about Billy, he's a top, top man," Johnson said.
"I wouldn't speak ill of him at all.
"I'm looking forward to seeing him actually.
"I've got fond memories of him, he built a great atmosphere in the dressing room."
The Shaymen moved four points clear thanks to Tuesday night's 1-0 win over Grimsby.
"I think it was a great win, we owed them one after the late goal last week," said Johnson.
"They're a decent, physical side. We knew what they were going to do, and worked hard all week on it, and I think we nullified all their threats really well.
"We were gearing ourselves up for it, we knew it was a massive game, especially going top and we wanted to continue that momentum."
Johnson is delighted at how the season is going.
"It's brilliant. The gaffer's keeping us all grounded, we've had a mentality all season that we'll just look at the next game and that's all we're going to do," he said.
"I think a bad result wouldn't harm us if it does happen, we're just going to keep ticking them off one by one, and hopefully continue.
"I've played for this club when we've been in 14th, 15th, so looking at the table now, it puts a smile on everyone's face, everyone comes in buzzing.
"Obviously the gaffer says 'don't look at the league table' but it's hard not to. It's really pleasing."
When asked what he puts The Shaymen being top of the table down to, Johnson said: "Hard work. It probably starts from the gaffer bringing in the right people at the right time.
"This season he's recruited really well.
"We've got great momentum, it feels like there's a really good buzz around the place everywhere, that's fans, staff, players, we've got a good dressing room as usual and it's just momentum that's keeping us going."
The Town keeper says this is the best Halifax team he has played in during his time at the club.
"Definitely, it can't not be at the minute," he said.
"We play some really good stuff, and it's got everyone going in the right direction.
"The work the lads put in, each and every game, you see Greeny coming off absolutely knackered every game, Ty (Warren), Jay Benn, Billy up-front never stops.
"It's all of them really, they never stop running. It's great to see."
The win over Grimsby was Halifax's 13th clean sheet of the season.
"I'm going to have to look what my best has been, I think I did quite a few under Jamie Fullarton," said Johnson.
"We've got 13 altogether, 11 in the league, and we haven't conceded too many.
"I think we needed the back-to-back clean sheets too, that's great."
And Johnson is confident The Shaymen can maintain the form they have shown so far over the second-half of the season.
"We've just got to keep grounded," he said.
"It's the feel-good factor, and if we keep that going through the season and not let one bad result, which I'm sure there's going to be somewhere down the line, affect us too much then we can keep going and going."